diff --git a/pyopencl/scan.py b/pyopencl/scan.py
index 66a46c0a2b3addc12aa9708dccbc9e9e396fd741..9d65c805f5350a8932dfae7637753566c305c2ba 100644
--- a/pyopencl/scan.py
+++ b/pyopencl/scan.py
@@ -785,7 +785,7 @@ _IGNORED_WORDS = set("""
 
         typedef for endfor if void while endwhile endfor endif else const printf
         None return bool n char true false ifdef pycl_printf str range assert
-        np iinfo max itemsize __packed__ struct restrict
+        np iinfo max itemsize __packed__ struct restrict ptrdiff_t
 
         set iteritems len setdefault