diff --git a/ldm/generate.py b/ldm/generate.py
index 7f7bd43397..6c45c02d47 100644
--- a/ldm/generate.py
+++ b/ldm/generate.py
@@ -965,6 +965,8 @@ class Generate:
         # Obtain the mask from the transparency channel
         if mask_image.mode == 'L':
             mask = mask_image
+        elif mask_image.mode in ('RGB', 'P'):
+            mask = mask_image.convert('L')
         else:
             # Obtain the mask from the transparency channel
             mask = Image.new(mode="L", size=mask_image.size, color=255)