diff --git a/spring-integration-core/src/main/java/org/springframework/integration/aggregator/CorrelatingMessageHandler.java b/spring-integration-core/src/main/java/org/springframework/integration/aggregator/CorrelatingMessageHandler.java
index 4050a0dbcf..22883c0908 100644
--- a/spring-integration-core/src/main/java/org/springframework/integration/aggregator/CorrelatingMessageHandler.java
+++ b/spring-integration-core/src/main/java/org/springframework/integration/aggregator/CorrelatingMessageHandler.java
@@ -166,6 +166,7 @@ public class CorrelatingMessageHandler extends AbstractMessageHandler implements
 
 		// TODO: INT-1117 - make the lock global?
 		Object lock = getLock(correlationKey);
+		Assert.notNull(lock, "Based on correlationKey '" + correlationKey + "' the returned lock is null"); // see INT-1940
 		synchronized (lock) {
 			MessageGroup group = messageStore.getMessageGroup(correlationKey);
 			if (group.canAdd(message)) {