diff --git a/platform/core-api/src/com/intellij/openapi/project/DumbModeTask.java b/platform/core-api/src/com/intellij/openapi/project/DumbModeTask.java
index 56fab1229f48..b7a0e0ee1cbf 100644
--- a/platform/core-api/src/com/intellij/openapi/project/DumbModeTask.java
+++ b/platform/core-api/src/com/intellij/openapi/project/DumbModeTask.java
@@ -20,9 +20,32 @@ import com.intellij.openapi.progress.ProgressIndicator;
 import org.jetbrains.annotations.NotNull;
 
 /**
+ * A task that should be executed in IDE dumb mode, via {@link DumbService#queueTask(DumbModeTask)}.
+ *
  * @author peter
  */
 public abstract class DumbModeTask implements Disposable {
+  private final Object myEquivalenceObject;
+
+  public DumbModeTask() {
+    myEquivalenceObject = this;
+  }
+
+  /**
+   * @param equivalenceObject see {@link #getEquivalenceObject()}
+   */
+  public DumbModeTask(@NotNull Object equivalenceObject) {
+    myEquivalenceObject = equivalenceObject;
+  }
+
+  /**
+   * @return an object whose {@link Object#equals(Object)} determines task equivalence. If several equivalent tasks are queued
+   * for dumb mode execution at once, only one of them will be executed. By default the task object itself is returned.
+   */
+  @NotNull
+  public final Object getEquivalenceObject() {
+    return myEquivalenceObject;
+  }
 
   public abstract void performInDumbMode(@NotNull ProgressIndicator indicator);
 
diff --git a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java
index 9d57ec867e83..55de678f3017 100644
--- a/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java
+++ b/platform/lang-impl/src/com/intellij/util/indexing/FileBasedIndexProjectHandler.java
@@ -20,7 +20,6 @@
 package com.intellij.util.indexing;
 
 import com.intellij.ide.IdeBundle;
-import com.intellij.ide.caches.FileContent;
 import com.intellij.ide.startup.StartupManagerEx;
 import com.intellij.openapi.application.ApplicationManager;
 import com.intellij.openapi.application.TransactionGuard;
@@ -38,7 +37,6 @@ import com.intellij.openapi.startup.StartupManager;
 import com.intellij.openapi.vfs.VfsUtilCore;
 import com.intellij.openapi.vfs.VirtualFile;
 import com.intellij.openapi.vfs.VirtualFileVisitor;
-import com.intellij.util.Consumer;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -141,7 +139,7 @@ public class FileBasedIndexProjectHandler extends AbstractProjectComponent imple
       return null;
     }
 
-    return new DumbModeTask() {
+    return new DumbModeTask(project.getComponent(FileBasedIndexProjectHandler.class)) {
       @Override
       public void performInDumbMode(@NotNull ProgressIndicator indicator) {
         final Collection<VirtualFile> files = index.getFilesToUpdate(project);
diff --git a/platform/platform-impl/src/com/intellij/openapi/project/DumbServiceImpl.java b/platform/platform-impl/src/com/intellij/openapi/project/DumbServiceImpl.java
index d30e47a2b84e..f6abe730fb68 100644
--- a/platform/platform-impl/src/com/intellij/openapi/project/DumbServiceImpl.java
+++ b/platform/platform-impl/src/com/intellij/openapi/project/DumbServiceImpl.java
@@ -46,7 +46,9 @@ import org.jetbrains.annotations.TestOnly;
 
 import javax.swing.*;
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.Map;
+import java.util.Set;
 
 public class DumbServiceImpl extends DumbService implements Disposable, ModificationTracker {
   private static final Logger LOG = Logger.getInstance("#com.intellij.openapi.project.DumbServiceImpl");
@@ -64,6 +66,7 @@ public class DumbServiceImpl extends DumbService implements Disposable, Modifica
   private boolean myUpdateFinishedQueued;
   private final DumbModeListener myPublisher;
   private long myModificationCount;
+  private final Set<Object> myQueuedEquivalences = new HashSet<>();
   private final Queue<DumbModeTask> myUpdatesQueue = new Queue<>(5);
 
   /**
@@ -99,6 +102,7 @@ public class DumbServiceImpl extends DumbService implements Disposable, Modifica
   public void dispose() {
     ApplicationManager.getApplication().assertIsDispatchThread();
     myUpdatesQueue.clear();
+    myQueuedEquivalences.clear();
     myRunWhenSmartQueue.clear();
     for (DumbModeTask task : new ArrayList<>(myProgresses.keySet())) {
       cancelTask(task);
@@ -190,6 +194,11 @@ public class DumbServiceImpl extends DumbService implements Disposable, Modifica
         return;
       }
 
+      if (!myQueuedEquivalences.add(task.getEquivalenceObject())) {
+        Disposer.dispose(task);
+        return;
+      }
+
       final DumbModePermission permission = schedulerPermission != null ? schedulerPermission : getEdtPermission();
 
       myProgresses.put(task, new ProgressIndicatorBase());
@@ -493,6 +502,7 @@ public class DumbServiceImpl extends DumbService implements Disposable, Modifica
         }
 
         DumbModeTask queuedTask = myUpdatesQueue.pullFirst();
+        myQueuedEquivalences.remove(queuedTask.getEquivalenceObject());
         ProgressIndicatorEx indicator = myProgresses.get(queuedTask);
         if (indicator.isCanceled()) {
           Disposer.dispose(queuedTask);