1 files changed, 1 insertions, 0 deletions
diff --git a/check.py b/check.py
index 2b594dd59..272e1394c 100755
--- a/check.py
+++ b/check.py
@@ -329,6 +329,7 @@ for t in sorted(os.listdir(os.path.join('test', 'passes'))):
     cmd = [os.path.join('bin', 'binaryen-shell'), opt, os.path.join('test', 'passes', t), '--print']
     print '    ', ' '.join(cmd)
     actual, err = subprocess.Popen(cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE).communicate()
+    assert not err, err
     fail_if_not_identical(actual, open(os.path.join('test', 'passes', passname + '.txt')).read())
 
 print '\n[ checking binaryen-shell testcases... ]\n'