diff --git a/logstash-core/src/main/java/org/logstash/common/io/DeadLetterQueueWriter.java b/logstash-core/src/main/java/org/logstash/common/io/DeadLetterQueueWriter.java
index 342c3ce751e..b321005b49b 100644
--- a/logstash-core/src/main/java/org/logstash/common/io/DeadLetterQueueWriter.java
+++ b/logstash-core/src/main/java/org/logstash/common/io/DeadLetterQueueWriter.java
@@ -254,7 +254,10 @@ public void close() {
             }
 
             try {
-                flushScheduler.shutdown();
+                // flushScheduler is null only if it's not explicitly started, which happens only in tests.
+                if (flushScheduler != null) {
+                    flushScheduler.shutdown();
+                }
             } catch (Exception e) {
                 logger.warn("Unable shutdown flush scheduler, ignoring", e);
             }