diff --git a/platform/util/src/com/intellij/util/keyFMap/DebugFMap.java b/platform/util/src/com/intellij/util/keyFMap/DebugFMap.java
new file mode 100644
index 000000000000..a56c414d20a6
--- /dev/null
+++ b/platform/util/src/com/intellij/util/keyFMap/DebugFMap.java
@@ -0,0 +1,63 @@
+// Copyright 2000-2020 JetBrains s.r.o. Use of this source code is governed by the Apache 2.0 license that can be found in the LICENSE file.
+package com.intellij.util.keyFMap;
+
+import com.intellij.openapi.util.Key;
+import com.intellij.util.containers.UnmodifiableHashMap;
+import org.jetbrains.annotations.NotNull;
+import org.jetbrains.annotations.Nullable;
+
+public class DebugFMap implements KeyFMap {
+  private final UnmodifiableHashMap<Key<?>, Object> myMap;
+
+  DebugFMap(@NotNull UnmodifiableHashMap<Key<?>, Object> map) {
+    myMap = map;
+  }
+
+  @Override
+  public @NotNull <V> KeyFMap plus(@NotNull Key<V> key, @NotNull V value) {
+    UnmodifiableHashMap<Key<?>, Object> newMap = myMap.with(key, value);
+    return newMap == myMap ? this : new DebugFMap(newMap);
+  }
+
+  @Override
+  public @NotNull KeyFMap minus(@NotNull Key<?> key) {
+    UnmodifiableHashMap<Key<?>, Object> newMap = myMap.without(key);
+    return newMap == myMap ? this : new DebugFMap(newMap);
+  }
+
+  @Override
+  public <V> @Nullable V get(@NotNull Key<V> key) {
+    @SuppressWarnings("unchecked") V value = (V)myMap.get(key);
+    return value;
+  }
+
+  @Override
+  public int size() {
+    return myMap.size();
+  }
+
+  @Override
+  public Key @NotNull [] getKeys() {
+    return myMap.keySet().toArray(new Key[0]);
+  }
+
+  @Override
+  public boolean isEmpty() {
+    return myMap.isEmpty();
+  }
+
+  @Override
+  public int getValueIdentityHashCode() {
+    final int[] hash = {0};
+    myMap.forEach((key, value) -> {
+      hash[0] = (hash[0] * 31 + key.hashCode()) * 31 + System.identityHashCode(value);
+    });
+    return hash[0];
+  }
+
+  @Override
+  public boolean equalsByReference(KeyFMap other) {
+    if (this.size() != other.size()) return false;
+    return myMap.entrySet().stream().noneMatch(entry -> entry.getValue() != other.get(entry.getKey()));
+  }
+}
diff --git a/platform/util/src/com/intellij/util/keyFMap/EmptyFMap.java b/platform/util/src/com/intellij/util/keyFMap/EmptyFMap.java
index d31661b27873..f8de371ec660 100644
--- a/platform/util/src/com/intellij/util/keyFMap/EmptyFMap.java
+++ b/platform/util/src/com/intellij/util/keyFMap/EmptyFMap.java
@@ -16,9 +16,11 @@
 package com.intellij.util.keyFMap;
 
 import com.intellij.openapi.util.Key;
+import com.intellij.util.containers.UnmodifiableHashMap;
 import org.jetbrains.annotations.NotNull;
 
 class EmptyFMap implements KeyFMap {
+  private static final boolean DEBUG_FMAP = Boolean.getBoolean("idea.keyfmap.debug.implementation"); 
   private static final Key[] EMPTY_KEYS_ARRAY = {};
 
   EmptyFMap() {
@@ -75,4 +77,8 @@ class EmptyFMap implements KeyFMap {
   public int hashCode() {
     return 0;
   }
+  
+  static KeyFMap create() {
+    return DEBUG_FMAP ? new DebugFMap(UnmodifiableHashMap.empty()) : new EmptyFMap();
+  }
 }
diff --git a/platform/util/src/com/intellij/util/keyFMap/KeyFMap.java b/platform/util/src/com/intellij/util/keyFMap/KeyFMap.java
index fe752dae9d3f..24b10a89805e 100644
--- a/platform/util/src/com/intellij/util/keyFMap/KeyFMap.java
+++ b/platform/util/src/com/intellij/util/keyFMap/KeyFMap.java
@@ -22,7 +22,7 @@ public interface KeyFMap {
   /**
    * An empty {@code KeyFMap}. No additional instances of empty {@code KeyFMap} should be created as they are indistinguishable.
    */
-  KeyFMap EMPTY_MAP = new EmptyFMap();
+  KeyFMap EMPTY_MAP = EmptyFMap.create();
 
   /**
    * Returns a {@code KeyFMap} which consists of the same elements as this {@code KeyFMap}, but