diff --git a/clang/lib/Frontend/InitHeaderSearch.cpp b/clang/lib/Frontend/InitHeaderSearch.cpp
index 0506975..d2fcc9a 100644
--- a/clang/lib/Frontend/InitHeaderSearch.cpp
+++ b/clang/lib/Frontend/InitHeaderSearch.cpp
@@ -105,7 +105,7 @@
 }  // end anonymous namespace.
 
 static bool CanPrefixSysroot(StringRef Path) {
-#if defined(LLVM_ON_WIN32)
+#if defined(_WIN32)
   return !Path.empty() && llvm::sys::path::is_separator(Path[0]);
 #else
   return llvm::sys::path::is_absolute(Path);