diff --git a/compiler/frontend/src/org/jetbrains/jet/util/slicedmap/TrackingSlicedMap.java b/compiler/frontend/src/org/jetbrains/jet/util/slicedmap/TrackingSlicedMap.java
index b8e0d5b3492..b2675f34abb 100644
--- a/compiler/frontend/src/org/jetbrains/jet/util/slicedmap/TrackingSlicedMap.java
+++ b/compiler/frontend/src/org/jetbrains/jet/util/slicedmap/TrackingSlicedMap.java
@@ -55,6 +55,7 @@ public class TrackingSlicedMap implements MutableSlicedMap {
         return delegate.getKeys(wrapSlice(slice));
     }
 
+    @NotNull
     @Override
     public Iterator<Map.Entry<SlicedMapKey<?, ?>, ?>> iterator() {
         Map<SlicedMapKey<?, ?>, Object> map = Maps.newHashMap();