diff --git a/src/hdchain.h b/src/hdchain.h
index d1ee445151..bb027b0257 100644
--- a/src/hdchain.h
+++ b/src/hdchain.h
@@ -74,6 +74,7 @@ public:
 
         // by swapping the members of two classes,
         // the two classes are effectively swapped
+        LOCK2(first.cs, second.cs);
         swap(first.nVersion, second.nVersion);
         swap(first.id, second.id);
         swap(first.fCrypted, second.fCrypted);