diff --git a/headers/flat.hpp/flat_map.hpp b/headers/flat.hpp/flat_map.hpp
index 6e285d0..27152f9 100644
--- a/headers/flat.hpp/flat_map.hpp
+++ b/headers/flat.hpp/flat_map.hpp
@@ -72,140 +72,140 @@ namespace flat_hpp
 
         template < typename InputIter >
         flat_map(InputIter first, InputIter last) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_map(sorted_range_t, InputIter first, InputIter last) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter >
         flat_map(sorted_unique_range_t, InputIter first, InputIter last) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         template < typename InputIter >
         flat_map(InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_map(sorted_range_t, InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter >
         flat_map(sorted_unique_range_t, InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_map(InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_map(sorted_range_t, InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_map(sorted_unique_range_t, InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
-        template < typename InputIter , typename Allocator >
+        template < typename InputIter, typename Allocator >
         flat_map(InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
-        template < typename InputIter , typename Allocator >
+        template < typename InputIter, typename Allocator >
         flat_map(sorted_range_t, InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
-        template < typename InputIter , typename Allocator >
+        template < typename InputIter, typename Allocator >
         flat_map(sorted_unique_range_t, InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         flat_map(std::initializer_list<value_type> ilist) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_map(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         flat_map(sorted_unique_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         flat_map(std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_map(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         flat_map(sorted_unique_range_t, std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_map(std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_map(sorted_range_t, std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_map(sorted_unique_range_t, std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_map(std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_map(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_map(sorted_unique_range_t, std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
@@ -401,32 +401,20 @@ namespace flat_hpp
 
         template < typename InputIter >
         void insert(InputIter first, InputIter last) {
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::sort(mid_iter, data_.end(), value_comp());
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
-            data_.erase(
-                std::unique(data_.begin(), data_.end(),
-                    detail::eq_compare<value_compare>(value_comp())),
-                data_.end());
+            insert_range_(first, last);
         }
 
         template < typename InputIter >
         void insert(sorted_range_t, InputIter first, InputIter last) {
-            assert(detail::is_sorted(first, last, value_comp()));
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
-            data_.erase(
-                std::unique(data_.begin(), data_.end(),
-                    detail::eq_compare<value_compare>(value_comp())),
-                data_.end());
+            insert_range_(sorted_range, first, last);
         }
 
         void insert(std::initializer_list<value_type> ilist) {
-            insert(ilist.begin(), ilist.end());
+            insert_range_(ilist.begin(), ilist.end());
         }
 
         void insert(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist.begin(), ilist.end());
+            insert_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename... Args >
@@ -611,6 +599,57 @@ namespace flat_hpp
         value_compare value_comp() const {
             return value_compare(key_comp());
         }
+    private:
+        template < typename Iter >
+        void from_range_(Iter first, Iter last) {
+            assert(data_.empty());
+            data_.insert(data_.end(), first, last);
+            std::sort(data_.begin(), data_.end(), value_comp());
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<value_compare>(value_comp())),
+                data_.end());
+        }
+
+        template < typename Iter >
+        void from_range_(sorted_range_t, Iter first, Iter last) {
+            assert(data_.empty());
+            assert(detail::is_sorted(first, last, value_comp()));
+            data_.insert(data_.end(), first, last);
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<value_compare>(value_comp())),
+                data_.end());
+        }
+
+        template < typename Iter >
+        void from_range_(sorted_unique_range_t, Iter first, Iter last) {
+            assert(data_.empty());
+            assert(detail::is_sorted_unique(first, last, value_comp()));
+            data_.insert(data_.end(), first, last);
+        }
+    private:
+        template < typename Iter >
+        void insert_range_(Iter first, Iter last) {
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::sort(mid_iter, data_.end(), value_comp());
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<value_compare>(value_comp())),
+                data_.end());
+        }
+
+        template < typename Iter >
+        void insert_range_(sorted_range_t, Iter first, Iter last) {
+            assert(detail::is_sorted(first, last, value_comp()));
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<value_compare>(value_comp())),
+                data_.end());
+        }
     private:
         container_type data_;
     };
diff --git a/headers/flat.hpp/flat_multimap.hpp b/headers/flat.hpp/flat_multimap.hpp
index 3220571..3ef707f 100644
--- a/headers/flat.hpp/flat_multimap.hpp
+++ b/headers/flat.hpp/flat_multimap.hpp
@@ -72,94 +72,94 @@ namespace flat_hpp
 
         template < typename InputIter >
         flat_multimap(InputIter first, InputIter last) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_multimap(sorted_range_t, InputIter first, InputIter last) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter >
         flat_multimap(InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_multimap(sorted_range_t, InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_multimap(InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_multimap(sorted_range_t, InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
-        template < typename InputIter , typename Allocator >
+        template < typename InputIter, typename Allocator >
         flat_multimap(InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
-        template < typename InputIter , typename Allocator >
+        template < typename InputIter, typename Allocator >
         flat_multimap(sorted_range_t, InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         flat_multimap(std::initializer_list<value_type> ilist) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_multimap(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         flat_multimap(std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_multimap(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multimap(std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multimap(sorted_range_t, std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multimap(std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multimap(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
@@ -351,24 +351,20 @@ namespace flat_hpp
 
         template < typename InputIter >
         void insert(InputIter first, InputIter last) {
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::sort(mid_iter, data_.end(), value_comp());
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            insert_range_(first, last);
         }
 
         template < typename InputIter >
         void insert(sorted_range_t, InputIter first, InputIter last) {
-            assert(detail::is_sorted(first, last, value_comp()));
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            insert_range_(sorted_range, first, last);
         }
 
         void insert(std::initializer_list<value_type> ilist) {
-            insert(ilist.begin(), ilist.end());
+            insert_range_(ilist.begin(), ilist.end());
         }
 
         void insert(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist.begin(), ilist.end());
+            insert_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename... Args >
@@ -553,6 +549,34 @@ namespace flat_hpp
         value_compare value_comp() const {
             return value_compare(key_comp());
         }
+    private:
+        template < typename Iter >
+        void from_range_(Iter first, Iter last) {
+            assert(data_.empty());
+            data_.insert(data_.end(), first, last);
+            std::sort(data_.begin(), data_.end(), value_comp());
+        }
+
+        template < typename Iter >
+        void from_range_(sorted_range_t, Iter first, Iter last) {
+            assert(data_.empty());
+            assert(detail::is_sorted(first, last, value_comp()));
+            data_.insert(data_.end(), first, last);
+        }
+    private:
+        template < typename Iter >
+        void insert_range_(Iter first, Iter last) {
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::sort(mid_iter, data_.end(), value_comp());
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+        }
+
+        template < typename Iter >
+        void insert_range_(sorted_range_t, Iter first, Iter last) {
+            assert(detail::is_sorted(first, last, value_comp()));
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+        }
     private:
         container_type data_;
     };
diff --git a/headers/flat.hpp/flat_multiset.hpp b/headers/flat.hpp/flat_multiset.hpp
index e493603..085e897 100644
--- a/headers/flat.hpp/flat_multiset.hpp
+++ b/headers/flat.hpp/flat_multiset.hpp
@@ -54,94 +54,94 @@ namespace flat_hpp
 
         template < typename InputIter >
         flat_multiset(InputIter first, InputIter last) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_multiset(sorted_range_t, InputIter first, InputIter last) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter >
         flat_multiset(InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_multiset(sorted_range_t, InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_multiset(InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_multiset(sorted_range_t, InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_multiset(InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_multiset(sorted_range_t, InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         flat_multiset(std::initializer_list<value_type> ilist) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_multiset(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         flat_multiset(std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_multiset(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multiset(std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multiset(sorted_range_t, std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multiset(std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_multiset(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
@@ -279,24 +279,20 @@ namespace flat_hpp
 
         template < typename InputIter >
         void insert(InputIter first, InputIter last) {
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::sort(mid_iter, data_.end(), value_comp());
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            insert_range_(first, last);
         }
 
         template < typename InputIter >
         void insert(sorted_range_t, InputIter first, InputIter last) {
-            assert(detail::is_sorted(first, last, value_comp()));
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            insert_range_(sorted_range, first, last);
         }
 
         void insert(std::initializer_list<value_type> ilist) {
-            insert(ilist.begin(), ilist.end());
+            insert_range_(ilist.begin(), ilist.end());
         }
 
         void insert(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist.begin(), ilist.end());
+            insert_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename... Args >
@@ -469,6 +465,34 @@ namespace flat_hpp
         value_compare value_comp() const {
             return value_compare(key_comp());
         }
+    private:
+        template < typename Iter >
+        void from_range_(Iter first, Iter last) {
+            assert(data_.empty());
+            data_.insert(data_.end(), first, last);
+            std::sort(data_.begin(), data_.end(), key_comp());
+        }
+
+        template < typename Iter >
+        void from_range_(sorted_range_t, Iter first, Iter last) {
+            assert(data_.empty());
+            assert(detail::is_sorted(first, last, key_comp()));
+            data_.insert(data_.end(), first, last);
+        }
+    private:
+        template < typename Iter >
+        void insert_range_(Iter first, Iter last) {
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::sort(mid_iter, data_.end(), key_comp());
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+        }
+
+        template < typename Iter >
+        void insert_range_(sorted_range_t, Iter first, Iter last) {
+            assert(detail::is_sorted(first, last, key_comp()));
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+        }
     private:
         container_type data_;
     };
diff --git a/headers/flat.hpp/flat_set.hpp b/headers/flat.hpp/flat_set.hpp
index 9e15a71..ff6c4d6 100644
--- a/headers/flat.hpp/flat_set.hpp
+++ b/headers/flat.hpp/flat_set.hpp
@@ -54,140 +54,140 @@ namespace flat_hpp
 
         template < typename InputIter >
         flat_set(InputIter first, InputIter last) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_set(sorted_range_t, InputIter first, InputIter last) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter >
         flat_set(sorted_unique_range_t, InputIter first, InputIter last) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         template < typename InputIter >
         flat_set(InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter >
         flat_set(sorted_range_t, InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter >
         flat_set(sorted_unique_range_t, InputIter first, InputIter last, const Compare& c)
         : base_type(c) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_set(InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_set(sorted_range_t, InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_set(sorted_unique_range_t, InputIter first, InputIter last, const Allocator& a)
         : data_(a) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_set(InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(first, last);
+            from_range_(first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_set(sorted_range_t, InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, first, last);
+            from_range_(sorted_range, first, last);
         }
 
         template < typename InputIter, typename Allocator >
         flat_set(sorted_unique_range_t, InputIter first, InputIter last, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_unique_range, first, last);
+            from_range_(sorted_unique_range, first, last);
         }
 
         flat_set(std::initializer_list<value_type> ilist) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_set(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         flat_set(sorted_unique_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         flat_set(std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         flat_set(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         flat_set(sorted_unique_range_t, std::initializer_list<value_type> ilist, const Compare& c)
         : base_type(c) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_set(std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_set(sorted_range_t, std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_set(sorted_unique_range_t, std::initializer_list<value_type> ilist, const Allocator& a)
         : data_(a) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_set(std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(ilist);
+            from_range_(ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_set(sorted_range_t, std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_range, ilist);
+            from_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
         flat_set(sorted_unique_range_t, std::initializer_list<value_type> ilist, const Compare& c, const Allocator& a)
         : base_type(c)
         , data_(a) {
-            insert(sorted_unique_range, ilist);
+            from_range_(sorted_unique_range, ilist.begin(), ilist.end());
         }
 
         template < typename Allocator >
@@ -329,32 +329,20 @@ namespace flat_hpp
 
         template < typename InputIter >
         void insert(InputIter first, InputIter last) {
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::sort(mid_iter, data_.end(), value_comp());
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
-            data_.erase(
-                std::unique(data_.begin(), data_.end(),
-                    detail::eq_compare<value_compare>(value_comp())),
-                data_.end());
+            insert_range_(first, last);
         }
 
         template < typename InputIter >
         void insert(sorted_range_t, InputIter first, InputIter last) {
-            assert(detail::is_sorted(first, last, value_comp()));
-            const auto mid_iter = data_.insert(data_.end(), first, last);
-            std::inplace_merge(data_.begin(), mid_iter, data_.end());
-            data_.erase(
-                std::unique(data_.begin(), data_.end(),
-                    detail::eq_compare<value_compare>(value_comp())),
-                data_.end());
+            insert_range_(sorted_range, first, last);
         }
 
         void insert(std::initializer_list<value_type> ilist) {
-            insert(ilist.begin(), ilist.end());
+            insert_range_(ilist.begin(), ilist.end());
         }
 
         void insert(sorted_range_t, std::initializer_list<value_type> ilist) {
-            insert(sorted_range, ilist.begin(), ilist.end());
+            insert_range_(sorted_range, ilist.begin(), ilist.end());
         }
 
         template < typename... Args >
@@ -527,6 +515,57 @@ namespace flat_hpp
         value_compare value_comp() const {
             return value_compare(key_comp());
         }
+    private:
+        template < typename Iter >
+        void from_range_(Iter first, Iter last) {
+            assert(data_.empty());
+            data_.insert(data_.end(), first, last);
+            std::sort(data_.begin(), data_.end(), key_comp());
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<key_compare>(key_comp())),
+                data_.end());
+        }
+
+        template < typename Iter >
+        void from_range_(sorted_range_t, Iter first, Iter last) {
+            assert(data_.empty());
+            assert(detail::is_sorted(first, last, key_comp()));
+            data_.insert(data_.end(), first, last);
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<key_compare>(key_comp())),
+                data_.end());
+        }
+
+        template < typename Iter >
+        void from_range_(sorted_unique_range_t, Iter first, Iter last) {
+            assert(data_.empty());
+            assert(detail::is_sorted_unique(first, last, key_comp()));
+            data_.insert(data_.end(), first, last);
+        }
+    private:
+        template < typename Iter >
+        void insert_range_(Iter first, Iter last) {
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::sort(mid_iter, data_.end(), key_comp());
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<key_compare>(key_comp())),
+                data_.end());
+        }
+
+        template < typename Iter >
+        void insert_range_(sorted_range_t, Iter first, Iter last) {
+            assert(detail::is_sorted(first, last, key_comp()));
+            const auto mid_iter = data_.insert(data_.end(), first, last);
+            std::inplace_merge(data_.begin(), mid_iter, data_.end());
+            data_.erase(
+                std::unique(data_.begin(), data_.end(),
+                    detail::eq_compare<key_compare>(key_comp())),
+                data_.end());
+        }
     private:
         container_type data_;
     };
diff --git a/untests/flat_map_tests.cpp b/untests/flat_map_tests.cpp
index 0cbbb4d..7ad0dc8 100644
--- a/untests/flat_map_tests.cpp
+++ b/untests/flat_map_tests.cpp
@@ -200,6 +200,15 @@ TEST_CASE("flat_map") {
             s3 = {{0,1}, {1,2}};
             REQUIRE(s3 == map_t{{0,1}, {1,2}});
         }
+
+        {
+            auto s0 = map_t(sorted_range, {{1,4},{2,3},{2,2},{3,1}});
+            REQUIRE(s0 == map_t{{1,4},{2,3},{3,1}});
+
+            vec_t v1({{1,4},{2,3},{2,2},{3,1}});
+            auto s1 = map_t(sorted_range, v1.begin(), v1.end());
+            REQUIRE(s1 == map_t{{1,4},{2,3},{3,1}});
+        }
     }
     SECTION("capacity") {
         using map_t = flat_map<int, unsigned>;
diff --git a/untests/flat_multimap_tests.cpp b/untests/flat_multimap_tests.cpp
index e37cd0a..461a22b 100644
--- a/untests/flat_multimap_tests.cpp
+++ b/untests/flat_multimap_tests.cpp
@@ -200,6 +200,15 @@ TEST_CASE("flat_multimap") {
             s3 = {{0,1}, {1,2}};
             REQUIRE(s3 == map_t{{0,1}, {1,2}});
         }
+
+        {
+            auto s0 = map_t(sorted_range, {{1,4},{2,3},{2,2},{3,1}});
+            REQUIRE(s0 == map_t{{1,4},{2,3},{2,2},{3,1}});
+
+            vec_t v1({{1,4},{2,3},{2,2},{3,1}});
+            auto s1 = map_t(sorted_range, v1.begin(), v1.end());
+            REQUIRE(s1 == map_t{{1,4},{2,3},{2,2},{3,1}});
+        }
     }
     SECTION("capacity") {
         using map_t = flat_multimap<int, unsigned>;
diff --git a/untests/flat_multiset_tests.cpp b/untests/flat_multiset_tests.cpp
index efe483d..2470283 100644
--- a/untests/flat_multiset_tests.cpp
+++ b/untests/flat_multiset_tests.cpp
@@ -186,6 +186,15 @@ TEST_CASE("flat_multiset") {
             s3 = {1,2,3};
             REQUIRE(s3 == set_t{1,2,3});
         }
+
+        {
+            auto s0 = set_t(sorted_range, {1,2,2,3});
+            REQUIRE(s0 == set_t{1,2,2,3});
+
+            vec_t v1({1,2,3,3});
+            auto s1 = set_t(sorted_range, v1.begin(), v1.end());
+            REQUIRE(s1 == set_t{1,2,3,3});
+        }
     }
     SECTION("capacity") {
         using set_t = flat_multiset<int>;
diff --git a/untests/flat_set_tests.cpp b/untests/flat_set_tests.cpp
index b2f4a7f..8b521b8 100644
--- a/untests/flat_set_tests.cpp
+++ b/untests/flat_set_tests.cpp
@@ -186,6 +186,15 @@ TEST_CASE("flat_set") {
             s3 = {1,2,3};
             REQUIRE(s3 == set_t{1,2,3});
         }
+
+        {
+            auto s0 = set_t(sorted_unique_range, {1,2,3});
+            REQUIRE(s0 == set_t{1,2,3});
+
+            vec_t v1({1,2,3});
+            auto s1 = set_t(sorted_unique_range, v1.begin(), v1.end());
+            REQUIRE(s1 == set_t{1,2,3});
+        }
     }
     SECTION("capacity") {
         using set_t = flat_set<int>;