diff --git a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexImpl.java b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexImpl.java
index 67e56536b4ba..63d7caa34549 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexImpl.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexImpl.java
@@ -988,12 +988,12 @@ public class FileBasedIndexImpl extends FileBasedIndex implements BaseComponent,
       final MapReduceIndex index = (MapReduceIndex)state.getIndex(indexId);
       assert index != null;
       final MemoryIndexStorage memStorage = (MemoryIndexStorage)index.getStorage();
-      index.getWriteLock().lock();
+      index.getReadLock().lock();
       try {
         memStorage.clearCaches();
       }
       finally {
-        index.getWriteLock().unlock();
+        index.getReadLock().unlock();
       }
     }
   }
diff --git a/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java b/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java
index 3776a65dcf87..b0afa3cdab0b 100644
--- a/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java
+++ b/platform/util/src/com/intellij/util/indexing/impl/MapReduceIndex.java
@@ -59,14 +59,13 @@ public abstract class MapReduceIndex<Key,Value, Input> implements InvertedIndex<
     @Override
     public void run() {
       try {
-        Lock writeLock = getWriteLock();
-        if (writeLock.tryLock()) {
-          try {
-            myStorage.clearCaches();
-          } finally {
-            writeLock.unlock();
-          }
+        getReadLock().lock();
+        try {
+          myStorage.clearCaches();
+        } finally {
+          getReadLock().unlock();
         }
+
         flush();
       } catch (Throwable e) {
         requestRebuild(e);