diff --git a/llvm/tools/llvm-ar/llvm-ar.cpp b/llvm/tools/llvm-ar/llvm-ar.cpp
--- a/llvm/tools/llvm-ar/llvm-ar.cpp
+++ b/llvm/tools/llvm-ar/llvm-ar.cpp
@@ -11,6 +11,7 @@
 //
 //===----------------------------------------------------------------------===//
 
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/ADT/StringSwitch.h"
 #include "llvm/ADT/Triple.h"
 #include "llvm/IR/LLVMContext.h"
@@ -1179,16 +1180,20 @@
   llvm::InitializeAllAsmParsers();
 
   Stem = sys::path::stem(ToolName);
-  if (Stem.contains_lower("dlltool"))
+  auto Is = [](StringRef Tool) {
+    auto I = Stem.rfind(Tool);
+    return I != StringRef::npos &&
+           (I + Tool.size() == Stem.size() || !isAlnum(Stem[I + Tool.size()]));
+  };
+
+  if (Is("dlltool"))
     return dlltoolDriverMain(makeArrayRef(argv, argc));
-
-  if (Stem.contains_lower("ranlib"))
+  if (Is("ranlib"))
     return ranlib_main(argc, argv);
-
-  if (Stem.contains_lower("lib"))
+  if (Is("lib"))
     return libDriverMain(makeArrayRef(argv, argc));
-
-  if (Stem.contains_lower("ar"))
+  if (Is("ar"))
     return ar_main(argc, argv);
+
   fail("not ranlib, ar, lib or dlltool");
 }