diff --git a/Demo/sgi/video/VFile.py b/Demo/sgi/video/VFile.py
index 2c99183ea7a5..d0eab0db35f3 100755
--- a/Demo/sgi/video/VFile.py
+++ b/Demo/sgi/video/VFile.py
@@ -416,6 +416,7 @@ def showpartframe(self, data, chromdata, (x,y,w,h)):
 			pmsize = bytes*8
 		elif self.format == 'compress':
 			data = self.decompress(data)
+			pmsize = 32
 		elif self.format in ('mono', 'grey4'):
 			if self.mustunpack:
 				if self.format == 'mono':