diff --git a/server/src/main/java/io/druid/segment/realtime/appenderator/AppenderatorImpl.java b/server/src/main/java/io/druid/segment/realtime/appenderator/AppenderatorImpl.java
index a9eb40611d0d..96a4accb3317 100644
--- a/server/src/main/java/io/druid/segment/realtime/appenderator/AppenderatorImpl.java
+++ b/server/src/main/java/io/druid/segment/realtime/appenderator/AppenderatorImpl.java
@@ -147,6 +147,7 @@ public class AppenderatorImpl implements Appenderator
   private volatile FileLock basePersistDirLock = null;
   private volatile FileChannel basePersistDirLockChannel = null;
   private AtomicBoolean closed = new AtomicBoolean(false);
+  private final Object sinkLock = new Object();
 
   AppenderatorImpl(
       DataSchema schema,
@@ -474,9 +475,10 @@ public ListenableFuture<Object> persistAll(@Nullable final Committer committer)
           indexesToPersist.add(Pair.of(hydrant, identifier));
         }
       }
-
-      if (sink.swappable()) {
-        indexesToPersist.add(Pair.of(sink.swap(), identifier));
+      synchronized (sinkLock) {
+        if (sink.swappable()) {
+          indexesToPersist.add(Pair.of(sink.swap(), identifier));
+        }
       }
     }
 
@@ -611,7 +613,8 @@ public ListenableFuture<SegmentsAndMetadata> push(
   private ListenableFuture<?> pushBarrier()
   {
     return intermediateTempExecutor.submit(
-        (Runnable) () -> pushExecutor.submit(() -> {})
+        (Runnable) () -> pushExecutor.submit(() -> {
+        })
     );
   }
 
@@ -619,8 +622,8 @@ private ListenableFuture<?> pushBarrier()
    * Merge segment, push to deep storage. Should only be used on segments that have been fully persisted. Must only
    * be run in the single-threaded pushExecutor.
    *
-   * @param identifier sink identifier
-   * @param sink       sink to push
+   * @param identifier    sink identifier
+   * @param sink          sink to push
    * @param useUniquePath true if the segment should be written to a path with a unique identifier
    *
    * @return segment descriptor, or null if the sink is no longer valid