diff --git a/headers/vmath.hpp/vmath_qua_fun.hpp b/headers/vmath.hpp/vmath_qua_fun.hpp
index b8f3280..5c83b55 100644
--- a/headers/vmath.hpp/vmath_qua_fun.hpp
+++ b/headers/vmath.hpp/vmath_qua_fun.hpp
@@ -165,6 +165,48 @@ namespace vmath_hpp::detail
 
 namespace vmath_hpp
 {
+    // +operator
+
+    template < typename T >
+    [[nodiscard]] constexpr qua<T> operator+(const qua<T>& xs) {
+        return xs;
+    }
+
+    // -operator
+
+    template < typename T >
+    [[nodiscard]] constexpr qua<T> operator-(const qua<T>& xs) {
+        return map_join([](T x){ return -x; }, xs);
+    }
+
+    // operator+
+
+    template < typename T >
+    [[nodiscard]] constexpr qua<T> operator+(const qua<T>& xs, const qua<T>& ys) {
+        return map_join([](T x, T y){ return x + y; }, xs, ys);
+    }
+
+    // operator+=
+
+    template < typename T >
+    constexpr qua<T>& operator+=(qua<T>& xs, const qua<T>& ys) {
+        return (xs = (xs + ys));
+    }
+
+    // operator-
+
+    template < typename T >
+    [[nodiscard]] constexpr qua<T> operator-(const qua<T>& xs, const qua<T>& ys) {
+        return map_join([](T x, T y){ return x - y; }, xs, ys);
+    }
+
+    // operator-=
+
+    template < typename T >
+    constexpr qua<T>& operator-=(qua<T>& xs, const qua<T>& ys) {
+        return (xs = (xs - ys));
+    }
+
     // operator==
 
     template < typename T >
diff --git a/untests/vmath_qua_fun_tests.cpp b/untests/vmath_qua_fun_tests.cpp
index 4f02c92..fc61a1c 100644
--- a/untests/vmath_qua_fun_tests.cpp
+++ b/untests/vmath_qua_fun_tests.cpp
@@ -39,4 +39,24 @@ TEST_CASE("vmath/qua_fun") {
             return acc + x;
         }, qua{1,2,3,4}) == 10);
     }
+
+    SUBCASE("Operators") {
+        STATIC_REQUIRE(+qua(1,-2,3,-4) == qua(1,-2,3,-4));
+        STATIC_REQUIRE(-qua(1,-2,3,-4) == qua(-1,2,-3,4));
+
+        STATIC_REQUIRE(qua(1,2,3,4) + qua(3,4,5,6) == qua(4,6,8,10));
+        STATIC_REQUIRE(qua(1,2,3,4) - qua(3,5,7,9) == qua(-2,-3,-4,-5));
+
+        {
+            qua v{1,2,3,4};
+            REQUIRE(&v == &(v += qua{3,4,5,6}));
+            REQUIRE(v == qua{4,6,8,10});
+        }
+
+        {
+            qua v{1,2,3,4};
+            REQUIRE(&v == &(v -= qua{3,4,5,6}));
+            REQUIRE(v == qua{-2,-2,-2,-2});
+        }
+    }
 }