Index: clang/lib/Driver/ToolChains/MinGW.cpp
===================================================================
--- clang/lib/Driver/ToolChains/MinGW.cpp
+++ clang/lib/Driver/ToolChains/MinGW.cpp
@@ -160,7 +160,15 @@
   }
 
   CmdArgs.push_back("-o");
-  CmdArgs.push_back(Output.getFilename());
+  const char *OutputFile = Output.getFilename();
+#ifdef _WIN32
+  if (!llvm::sys::path::filename(OutputFile).contains('.'))
+    CmdArgs.push_back(Args.MakeArgString(Twine(OutputFile) + ".exe"));
+  else
+    CmdArgs.push_back(OutputFile);
+#else
+  CmdArgs.push_back(OutputFile);
+#endif
 
   Args.AddAllArgs(CmdArgs, options::OPT_e);
   // FIXME: add -N, -n flags