diff --git a/clang/test/Driver/cl.c b/clang/test/Driver/cl.c
index c141c2f8c0f3..13cd9c26195c 100644
--- a/clang/test/Driver/cl.c
+++ b/clang/test/Driver/cl.c
@@ -1,14 +1,18 @@
+// Note: we have to quote the /? option, otherwise some shells will try
+// to expand the ? into a one-letter filename in the root directory,
+// and make the test fail if such a file or directory exists.
+
 // Check that clang-cl options are not available by default.
 // RUN: %clang -help | FileCheck %s -check-prefix=DEFAULT
 // DEFAULT-NOT: CL.EXE COMPATIBILITY OPTIONS
 // DEFAULT-NOT: {{/[?]}}
 // DEFAULT-NOT: /help
-// RUN: not %clang /?
+// RUN: not %clang "/?"
 // RUN: not %clang -?
 // RUN: not %clang /help
 
-// Check that /? and /help are available as clang-cl options.
-// RUN: %clang_cl /? | FileCheck %s -check-prefix=CL
+// Check that "/?" and /help are available as clang-cl options.
+// RUN: %clang_cl "/?" | FileCheck %s -check-prefix=CL
 // RUN: %clang_cl /help | FileCheck %s -check-prefix=CL
 // RUN: %clang_cl -help | FileCheck %s -check-prefix=CL
 // CL: CL.EXE COMPATIBILITY OPTIONS