diff --git a/offlineimap/init.py b/offlineimap/init.py
index 8aebb23..9e23fdd 100644
--- a/offlineimap/init.py
+++ b/offlineimap/init.py
@@ -213,7 +213,7 @@ class OfflineImap:
             if not ('thread' in options.debugtype.split(',') \
                     and options.singlethreading):
                 ui._msg("Debug mode: Forcing to singlethreaded.")
-                options.singlethreaded = True
+                options.singlethreading = True
 
             for type in options.debugtype.split(','):
                 type = type.strip()