diff --git a/pyopencl/__init__.py b/pyopencl/__init__.py
index 9f9b6c92c4771cb1af2e7d610985f17df48050ec..12af8f358f145c23ea28be397e53cd1b45d80f84 100644
--- a/pyopencl/__init__.py
+++ b/pyopencl/__init__.py
@@ -382,7 +382,7 @@ class Program(object):
         import sys
         if sys.platform.startswith("win"):
             # not sure how to escape that
-            assert '"' not in s
+            assert b'"' not in s
             return b'"' + s + b'"'
         else:
             return b"'" + s.replace(b"'", b"'\"'\"'") + b"'"