diff --git a/loopy/check.py b/loopy/check.py
index 6ac058b933a8884887c3e6bdc530ce058617f9e0..9115d740e8c2b6b3f721706306f2ad673ec745ed 100644
--- a/loopy/check.py
+++ b/loopy/check.py
@@ -93,7 +93,7 @@ def check_insn_attributes(kernel):
         if not no_sync_with_scopes <= VALID_NOSYNC_SCOPES:
             raise LoopyError("insn '%s' has invalid nosync scopes: %s"
                     % (insn.id,
-                       ", ".join(VALID_NOSYNC_SCOPES - no_sync_with_scopes)))
+                       ", ".join(no_sync_with_scopes - VALID_NOSYNC_SCOPES)))
 
 
 def check_loop_priority_inames_known(kernel):