diff --git a/clang/lib/Frontend/InitHeaderSearch.cpp b/clang/lib/Frontend/InitHeaderSearch.cpp
index 3da38fb04631..c552512dc957 100644
--- a/clang/lib/Frontend/InitHeaderSearch.cpp
+++ b/clang/lib/Frontend/InitHeaderSearch.cpp
@@ -118,7 +118,12 @@ void InitHeaderSearch::AddPath(const llvm::Twine &Path,
 
   // Handle isysroot.
   if ((Group == System || Group == CXXSystem) && !IgnoreSysRoot &&
+#if defined(_WIN32)
+      !MappedPathStr.empty() &&
+      llvm::sys::path::is_separator(MappedPathStr[0]) &&
+#else
       llvm::sys::path::is_absolute(MappedPathStr) &&
+#endif
       IsNotEmptyOrRoot) {
     MappedPathStorage.clear();
     MappedPathStr =
diff --git a/clang/test/PCH/reloc.c b/clang/test/PCH/reloc.c
index f15c77682fd8..fd78feba6047 100644
--- a/clang/test/PCH/reloc.c
+++ b/clang/test/PCH/reloc.c
@@ -1,7 +1,7 @@
 // RUN: %clang_cc1 -emit-pch -o %t -relocatable-pch -isysroot %S/libroot %S/libroot/usr/include/reloc.h
 // RUN: %clang_cc1 -include-pch %t -isysroot %S/libroot %s -verify
 // RUN: not %clang_cc1 -include-pch %t %s
-// XFAIL: mingw,win32
+
 #include <reloc.h>
 
 int x = 2; // expected-error{{redefinition}}