diff --git a/src/main/java/org/qortal/controller/Synchronizer.java b/src/main/java/org/qortal/controller/Synchronizer.java
index 4e8aa33c..e9090cf0 100644
--- a/src/main/java/org/qortal/controller/Synchronizer.java
+++ b/src/main/java/org/qortal/controller/Synchronizer.java
@@ -307,6 +307,11 @@ public class Synchronizer extends Thread {
 				}
 			}
 
+			if (!running) {
+				// We've stopped
+				return SynchronizationResult.SHUTTING_DOWN;
+			}
+
 			// Has our chain tip changed?
 			BlockData newChainTip;