diff --git a/on-modify.timewarrior b/on-modify.timewarrior
index 6ca0b08..0e7500c 100644
--- a/on-modify.timewarrior
+++ b/on-modify.timewarrior
@@ -42,7 +42,7 @@ old = json.loads(sys.stdin.readline())
 new = json.loads(sys.stdin.readline())
 print(json.dumps(new))
 
-def get_timew_name_from_json(json_obj):
+def extract_timew_tags_from(json_obj):
     # Extract attributes for use as tags.
     tags = [json_obj['description']]
 
@@ -52,7 +52,7 @@ def get_timew_name_from_json(json_obj):
     if 'tags' in json_obj:
         tags.extend(json_obj['tags'])
 
-    return ' '.join(['"%s"' % tag for tag in tags]).encode('utf-8').strip()
+    return ' '.join(['"{0}"'.format(tag) for tag in tags]).encode('utf-8').strip()
 
 start_or_stop = ''
 
@@ -65,19 +65,15 @@ elif 'start' not in new and 'start' in old:
     start_or_stop = 'stop'
 
 if start_or_stop:
-    combined = get_timew_name_from_json(new)
+    combined = extract_timew_tags_from(new)
 
-    command = 'timew {0} {1} :yes'.format(start_or_stop, combined)
-    subprocess.call(shlex.split(command))
+    subprocess.call(shlex.split('timew {0} {1} :yes'.format(start_or_stop, combined)))
 
 # Modifications to task other than start/stop
 elif 'start' in new and 'start' in old:
-    old_combined = get_timew_name_from_json(old)
-    new_combined = get_timew_name_from_json(new)
+    old_combined = extract_timew_tags_from(old)
+    new_combined = extract_timew_tags_from(new)
 
     if old_combined != new_combined:
-        command = 'timew stop {0} :yes'.format(old_combined)
-        subprocess.call(shlex.split(command))
-
-        command = 'timew start {0} :yes'.format(new_combined)
-        subprocess.call(shlex.split(command))
+        subprocess.call(shlex.split('timew untag @1 {0} :yes'.format(old_combined)))
+        subprocess.call(shlex.split('timew tag @1 {0} :yes'.format(new_combined)))