diff --git a/clang/test/Misc/serialized-diags-empty-filename.c b/clang/test/Misc/serialized-diags-empty-filename.c
index e86108414273..32a9156e0215 100644
--- a/clang/test/Misc/serialized-diags-empty-filename.c
+++ b/clang/test/Misc/serialized-diags-empty-filename.c
@@ -1,5 +1,5 @@
 // RUN: rm -f %t.diag
-// RUN: not %clang -c %s --serialize-diagnostics %t.diag
+// RUN: not %clang -c %s --serialize-diagnostics %t.diag -o /dev/null
 // RUN: c-index-test -read-diagnostics %t.diag 2>&1 | FileCheck %s
 
 # 1 "" 1