diff --git a/platform/util/src/com/intellij/util/keyFMap/MapBackedFMap.java b/platform/util/src/com/intellij/util/keyFMap/MapBackedFMap.java
index 1622132f0118..4f9ba3e400bd 100644
--- a/platform/util/src/com/intellij/util/keyFMap/MapBackedFMap.java
+++ b/platform/util/src/com/intellij/util/keyFMap/MapBackedFMap.java
@@ -36,6 +36,7 @@ class MapBackedFMap extends TIntObjectHashMap<Object> implements KeyFMap {
   }
 
   MapBackedFMap(@NotNull int[] keys, int newKey, @NotNull Object[] values, @NotNull Object newValue) {
+    super(keys.length + 1);
     for (int i = 0; i < keys.length; i++) {
       int key = keys[i];
       Object value = values[i];