diff --git a/llvm/test/FileCheck/allow-unused-prefixes.txt b/llvm/test/FileCheck/allow-unused-prefixes.txt
--- a/llvm/test/FileCheck/allow-unused-prefixes.txt
+++ b/llvm/test/FileCheck/allow-unused-prefixes.txt
@@ -1,6 +1,6 @@
-; RUN: not FileCheck --allow-unused-prefixes=false --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 2>&1 | FileCheck --check-prefix=MISSING-ONE %s
-; RUN: not FileCheck --allow-unused-prefixes=false --check-prefixes=P1,P2,P3 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 2>&1 | FileCheck --check-prefix=MISSING-MORE %s
-; RUN: FileCheck --allow-unused-prefixes=true  --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 
+; RUN: %ProtectFileCheckOutput not FileCheck --allow-unused-prefixes=false --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 2>&1 | FileCheck --check-prefix=MISSING-ONE %s
+; RUN: %ProtectFileCheckOutput not FileCheck --allow-unused-prefixes=false --check-prefixes=P1,P2,P3 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 2>&1 | FileCheck --check-prefix=MISSING-MORE %s
+; RUN: %ProtectFileCheckOutput FileCheck --allow-unused-prefixes=true  --check-prefixes=P1,P2 --input-file %S/Inputs/one-check.txt %S/Inputs/one-check.txt 
 
 ;; Note: the default will be changed to 'false', at which time this run line
 ;; should be changed accordingly.