diff --git a/platform/platform-api/src/com/intellij/util/concurrency/QueueProcessor.java b/platform/platform-api/src/com/intellij/util/concurrency/QueueProcessor.java
index 6f99bce00008..834e4d241bc2 100644
--- a/platform/platform-api/src/com/intellij/util/concurrency/QueueProcessor.java
+++ b/platform/platform-api/src/com/intellij/util/concurrency/QueueProcessor.java
@@ -145,7 +145,9 @@ public class QueueProcessor<T> {
   }
 
   public void add(T t, ModalityState state) {
-    myModalityState.put(new MyOverrideEquals(t), state);
+    synchronized (myQueue) {
+      myModalityState.put(new MyOverrideEquals(t), state);
+    }
     doAdd(t, false);
   }