diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java b/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java
index f1a7e859cd..6d1971e2d4 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ChangeIndexer.java
@@ -18,6 +18,7 @@ import static com.google.gerrit.server.extensions.events.EventUtil.logEventListe
 import static com.google.gerrit.server.git.QueueProvider.QueueType.BATCH;
 
 import com.google.common.base.Function;
+import com.google.common.base.Objects;
 import com.google.common.util.concurrent.Atomics;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListenableFuture;
@@ -50,7 +51,9 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.Callable;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ExecutionException;
 import java.util.concurrent.Future;
 import java.util.concurrent.atomic.AtomicReference;
@@ -111,6 +114,11 @@ public class ChangeIndexer {
   private final StalenessChecker stalenessChecker;
   private final boolean autoReindexIfStale;
 
+  private final Set<IndexTask> queuedIndexTasks =
+      Collections.newSetFromMap(new ConcurrentHashMap<>());
+  private final Set<ReindexIfStaleTask> queuedReindexIfStaleTasks =
+      Collections.newSetFromMap(new ConcurrentHashMap<>());
+
   @AssistedInject
   ChangeIndexer(
       @GerritServerConfig Config cfg,
@@ -178,7 +186,11 @@ public class ChangeIndexer {
   @SuppressWarnings("deprecation")
   public com.google.common.util.concurrent.CheckedFuture<?, IOException> indexAsync(
       Project.NameKey project, Change.Id id) {
-    return submit(new IndexTask(project, id));
+    IndexTask task = new IndexTask(project, id);
+    if (queuedIndexTasks.add(task)) {
+      return submit(task);
+    }
+    return Futures.immediateCheckedFuture(null);
   }
 
   /**
@@ -309,7 +321,11 @@ public class ChangeIndexer {
   @SuppressWarnings("deprecation")
   public com.google.common.util.concurrent.CheckedFuture<Boolean, IOException> reindexIfStale(
       Project.NameKey project, Change.Id id) {
-    return submit(new ReindexIfStaleTask(project, id), batchExecutor);
+    ReindexIfStaleTask task = new ReindexIfStaleTask(project, id);
+    if (queuedReindexIfStaleTasks.add(task)) {
+      return submit(task, batchExecutor);
+    }
+    return Futures.immediateCheckedFuture(false);
   }
 
   private void autoReindexIfStale(ChangeData cd) {
@@ -351,6 +367,8 @@ public class ChangeIndexer {
 
     protected abstract T callImpl(Provider<ReviewDb> db) throws Exception;
 
+    protected abstract void remove();
+
     @Override
     public abstract String toString();
 
@@ -405,15 +423,35 @@ public class ChangeIndexer {
 
     @Override
     public Void callImpl(Provider<ReviewDb> db) throws Exception {
+      remove();
       ChangeData cd = newChangeData(db.get(), project, id);
       index(cd);
       return null;
     }
 
+    @Override
+    public int hashCode() {
+      return Objects.hashCode(IndexTask.class, id.get());
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (!(obj instanceof IndexTask)) {
+        return false;
+      }
+      IndexTask other = (IndexTask) obj;
+      return id.get() == other.id.get();
+    }
+
     @Override
     public String toString() {
       return "index-change-" + id;
     }
+
+    @Override
+    protected void remove() {
+      queuedIndexTasks.remove(this);
+    }
   }
 
   // Not AbstractIndexTask as it doesn't need ReviewDb.
@@ -445,6 +483,7 @@ public class ChangeIndexer {
 
     @Override
     public Boolean callImpl(Provider<ReviewDb> db) throws Exception {
+      remove();
       try {
         if (stalenessChecker.isStale(id)) {
           index(newChangeData(db.get(), project, id));
@@ -464,10 +503,29 @@ public class ChangeIndexer {
       return false;
     }
 
+    @Override
+    public int hashCode() {
+      return Objects.hashCode(ReindexIfStaleTask.class, id.get());
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (!(obj instanceof ReindexIfStaleTask)) {
+        return false;
+      }
+      ReindexIfStaleTask other = (ReindexIfStaleTask) obj;
+      return id.get() == other.id.get();
+    }
+
     @Override
     public String toString() {
       return "reindex-if-stale-change-" + id;
     }
+
+    @Override
+    protected void remove() {
+      queuedReindexIfStaleTasks.remove(this);
+    }
   }
 
   private boolean isCausedByRepositoryNotFoundException(Throwable throwable) {
diff --git a/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ReindexAfterRefUpdate.java b/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ReindexAfterRefUpdate.java
index a2a4507cc9..a59557f375 100644
--- a/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ReindexAfterRefUpdate.java
+++ b/gerrit-server/src/main/java/com/google/gerrit/server/index/change/ReindexAfterRefUpdate.java
@@ -17,6 +17,7 @@ package com.google.gerrit.server.index.change;
 import static com.google.common.util.concurrent.MoreExecutors.directExecutor;
 import static com.google.gerrit.server.query.change.ChangeData.asChanges;
 
+import com.google.common.base.Objects;
 import com.google.common.util.concurrent.FutureCallback;
 import com.google.common.util.concurrent.Futures;
 import com.google.common.util.concurrent.ListeningExecutorService;
@@ -42,8 +43,11 @@ import com.google.gwtorm.server.OrmException;
 import com.google.inject.Inject;
 import com.google.inject.Provider;
 import java.io.IOException;
+import java.util.Collections;
 import java.util.List;
+import java.util.Set;
 import java.util.concurrent.Callable;
+import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.Future;
 import org.eclipse.jgit.lib.Config;
 import org.slf4j.Logger;
@@ -62,6 +66,8 @@ public class ReindexAfterRefUpdate implements GitReferenceUpdatedListener {
   private final ListeningExecutorService executor;
   private final boolean enabled;
 
+  private final Set<Index> queuedIndexTasks = Collections.newSetFromMap(new ConcurrentHashMap<>());
+
   @Inject
   ReindexAfterRefUpdate(
       @GerritServerConfig Config cfg,
@@ -109,9 +115,12 @@ public class ReindexAfterRefUpdate implements GitReferenceUpdatedListener {
           @Override
           public void onSuccess(List<Change> changes) {
             for (Change c : changes) {
-              // Don't retry indefinitely; if this fails changes may be stale.
-              @SuppressWarnings("unused")
-              Future<?> possiblyIgnoredError = executor.submit(new Index(event, c.getId()));
+              Index task = new Index(event, c.getId());
+              if (queuedIndexTasks.add(task)) {
+                // Don't retry indefinitely; if this fails changes may be stale.
+                @SuppressWarnings("unused")
+                Future<?> possiblyIgnoredError = executor.submit(task);
+              }
             }
           }
 
@@ -141,6 +150,8 @@ public class ReindexAfterRefUpdate implements GitReferenceUpdatedListener {
     }
 
     protected abstract V impl(RequestContext ctx) throws Exception;
+
+    protected abstract void remove();
   }
 
   private class GetChanges extends Task<List<Change>> {
@@ -165,6 +176,9 @@ public class ReindexAfterRefUpdate implements GitReferenceUpdatedListener {
           + " update of project "
           + event.getProjectName();
     }
+
+    @Override
+    protected void remove() {}
   }
 
   private class Index extends Task<Void> {
@@ -179,6 +193,7 @@ public class ReindexAfterRefUpdate implements GitReferenceUpdatedListener {
     protected Void impl(RequestContext ctx) throws OrmException, IOException {
       // Reload change, as some time may have passed since GetChanges.
       ReviewDb db = ctx.getReviewDbProvider().get();
+      remove();
       try {
         Change c =
             notesFactory
@@ -191,9 +206,28 @@ public class ReindexAfterRefUpdate implements GitReferenceUpdatedListener {
       return null;
     }
 
+    @Override
+    public int hashCode() {
+      return Objects.hashCode(Index.class, id.get());
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+      if (!(obj instanceof Index)) {
+        return false;
+      }
+      Index other = (Index) obj;
+      return id.get() == other.id.get();
+    }
+
     @Override
     public String toString() {
       return "Index change " + id.get() + " of project " + event.getProjectName();
     }
+
+    @Override
+    protected void remove() {
+      queuedIndexTasks.remove(this);
+    }
   }
 }