diff --git a/llvm/utils/lit/lit/TestRunner.py b/llvm/utils/lit/lit/TestRunner.py
--- a/llvm/utils/lit/lit/TestRunner.py
+++ b/llvm/utils/lit/lit/TestRunner.py
@@ -640,7 +640,7 @@
 
     procs = []
     proc_not_counts = []
-    default_stdin = subprocess.PIPE
+    default_stdin = None
     stderrTempFiles = []
     opened_files = []
     named_temp_files = []