diff --git a/kaldb/src/main/java/com/slack/kaldb/logstore/LuceneIndexStoreImpl.java b/kaldb/src/main/java/com/slack/kaldb/logstore/LuceneIndexStoreImpl.java
index f60d8a93b6..935056bd3c 100644
--- a/kaldb/src/main/java/com/slack/kaldb/logstore/LuceneIndexStoreImpl.java
+++ b/kaldb/src/main/java/com/slack/kaldb/logstore/LuceneIndexStoreImpl.java
@@ -257,11 +257,16 @@ private void handleNonFatal(Throwable ex) {
   public void addMessage(LogMessage message) {
     try {
       messagesReceivedCounter.increment();
-      if (indexWriter.isPresent()) {
-        indexWriter.get().addDocument(documentBuilder.fromMessage(message));
-      } else {
-        LOG.error("IndexWriter should never be null when adding a message");
-        throw new IllegalStateException("IndexWriter should never be null when adding a message");
+      indexWriterLock.lock();
+      try {
+        if (indexWriter.isPresent()) {
+          indexWriter.get().addDocument(documentBuilder.fromMessage(message));
+        } else {
+          LOG.error("IndexWriter should never be null when adding a message");
+          throw new IllegalStateException("IndexWriter should never be null when adding a message");
+        }
+      } finally {
+        indexWriterLock.unlock();
       }
     } catch (FieldDefMismatchException | IllegalArgumentException e) {
       LOG.error(String.format("Indexing message %s failed with error:", message), e);