diff --git a/src/message.cc b/src/message.cc
index 3f68667..b703576 100644
--- a/src/message.cc
+++ b/src/message.cc
@@ -763,7 +763,7 @@ int messageListRepositoryAddExtra(int messageListId, const char* path)
     }
 
     if (messageListId == 0) {
-        messageListId == _messageListRepositoryState->nextTemporaryMessageListId++;
+        messageListId = _messageListRepositoryState->nextTemporaryMessageListId++;
     }
 
     _messageListRepositoryState->temporaryMessageLists[messageListId] = messageList;