diff --git a/setup.py b/setup.py
--- a/setup.py
+++ b/setup.py
@@ -274,7 +274,7 @@
         if err or returncode != 0:
             printf("stderr from '%s':" % (' '.join(cmd)), file=sys.stderr)
             printf(err, file=sys.stderr)
-            return ''
+            return b''
         return out