diff --git a/lib/Frontend/CompilerInvocation.cpp b/lib/Frontend/CompilerInvocation.cpp
index f5079dd..581d56d 100644
--- a/lib/Frontend/CompilerInvocation.cpp
+++ b/lib/Frontend/CompilerInvocation.cpp
@@ -299,14 +299,14 @@
   using namespace options;
   bool Success = true;
 
-  Opts.OptimizationLevel = getOptimizationLevel(Args, IK, Diags);
-  unsigned MaxOptLevel = 3;
-  if (Opts.OptimizationLevel > MaxOptLevel) {
-    // If the optimization level is not supported, fall back on the default optimization
-    Diags.Report(diag::warn_drv_optimization_value)
-        << Args.getLastArg(OPT_O)->getAsString(Args) << "-O" << MaxOptLevel;
-    Opts.OptimizationLevel = MaxOptLevel;
+  unsigned OptLevel = getOptimizationLevel(Args, IK, Diags);
+  if (OptLevel > 3) {
+    Diags.Report(diag::err_drv_invalid_value)
+      << Args.getLastArg(OPT_O)->getAsString(Args) << OptLevel;
+    OptLevel = 3;
+    Success = false;
   }
+  Opts.OptimizationLevel = OptLevel;
 
   // We must always run at least the always inlining pass.
   Opts.setInlining(