diff --git a/misskaty/helper/tools.py b/misskaty/helper/tools.py
index 9caaca6f..0ea36179 100644
--- a/misskaty/helper/tools.py
+++ b/misskaty/helper/tools.py
@@ -205,7 +205,7 @@ async def gen_trans_image(msg, path):
 
     # put mask into alpha channel
     result = img.copy()
-    result = cv2.cvtColor(result, cv2.COLOR_BGR2BGRA))
+    result = cv2.cvtColor(result, cv2.COLOR_BGR2BGRA)
     result[:, :, 3] = mask
 
     # save resulting masked image