diff --git a/clang/test/CodeGen/debug-prefix-map.c b/clang/test/CodeGen/debug-prefix-map.c
--- a/clang/test/CodeGen/debug-prefix-map.c
+++ b/clang/test/CodeGen/debug-prefix-map.c
@@ -1,10 +1,10 @@
-// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-NO-MAIN-FILE-NAME
-// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH=empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-EVIL
-// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - -main-file-name debug-prefix-map.c | FileCheck %s
-// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - -fdebug-compilation-dir %p | FileCheck %s -check-prefix CHECK-COMPILATION-DIR
-// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty %s -emit-llvm -o - -isysroot %p -debugger-tuning=lldb | FileCheck %s -check-prefix CHECK-SYSROOT
-// RUN: %clang -g -fdebug-prefix-map=%p=/UNLIKELY_PATH/empty -S -c %s -emit-llvm -o - | FileCheck %s
-// RUN: %clang -g -ffile-prefix-map=%p=/UNLIKELY_PATH/empty -S -c %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{rootsep}UNLIKELY_PATH%{sep}empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-NO-MAIN-FILE-NAME
+// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{rootsep}UNLIKELY_PATH=empty %s -emit-llvm -o - | FileCheck %s -check-prefix CHECK-EVIL
+// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{rootsep}UNLIKELY_PATH%{sep}empty %s -emit-llvm -o - -main-file-name debug-prefix-map.c | FileCheck %s
+// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{rootsep}UNLIKELY_PATH%{sep}empty %s -emit-llvm -o - -fdebug-compilation-dir %p | FileCheck %s -check-prefix CHECK-COMPILATION-DIR
+// RUN: %clang_cc1 -debug-info-kind=standalone -fdebug-prefix-map=%p=%{rootsep}UNLIKELY_PATH%{sep}empty %s -emit-llvm -o - -isysroot %p -debugger-tuning=lldb | FileCheck %s -check-prefix CHECK-SYSROOT
+// RUN: %clang -g -fdebug-prefix-map=%p=%{rootsep}UNLIKELY_PATH%{sep}empty -S -c %s -emit-llvm -o - | FileCheck %s
+// RUN: %clang -g -ffile-prefix-map=%p=%{rootsep}UNLIKELY_PATH%{sep}empty -S -c %s -emit-llvm -o - | FileCheck %s
 
 #include "Inputs/stdio.h"
 
diff --git a/clang/test/lit.cfg.py b/clang/test/lit.cfg.py
--- a/clang/test/lit.cfg.py
+++ b/clang/test/lit.cfg.py
@@ -56,6 +56,16 @@
 config.substitutions.append(('%PATH%', config.environment['PATH']))
 
 
+if platform.system() == 'Windows':
+    root_sep = 'C:\\'
+else:
+    root_sep = os.path.sep
+
+config.substitutions.extend([
+    ('%{rootsep}', root_sep),
+    ('%{sep}', os.path.sep),
+])
+
 # For each occurrence of a clang tool name, replace it with the full path to
 # the build directory holding that tool.  We explicitly specify the directories
 # to search to ensure that we get the tools just built and not some random