diff --git a/src/img2pdf.py b/src/img2pdf.py
index 00be692..1dc01c4 100755
--- a/src/img2pdf.py
+++ b/src/img2pdf.py
@@ -858,6 +858,8 @@ class pdfdoc(object):
         image[PdfName.ColorSpace] = colorspace
         image[PdfName.BitsPerComponent] = depth
 
+        smask = None
+
         if color == Colorspace["CMYK;I"]:
             # Inverts all four channels
             image[PdfName.Decode] = [1, 0, 1, 0, 1, 0, 1, 0]