diff --git a/clang/lib/CodeGen/CodeGenAction.cpp b/clang/lib/CodeGen/CodeGenAction.cpp
index 6a184e0ef921..dd32167b8477 100644
--- a/clang/lib/CodeGen/CodeGenAction.cpp
+++ b/clang/lib/CodeGen/CodeGenAction.cpp
@@ -23,6 +23,7 @@
 #include "llvm/Module.h"
 #include "llvm/Pass.h"
 #include "llvm/ADT/OwningPtr.h"
+#include "llvm/ADT/SmallString.h"
 #include "llvm/Bitcode/ReaderWriter.h"
 #include "llvm/Support/IRReader.h"
 #include "llvm/Support/MemoryBuffer.h"
@@ -393,8 +394,17 @@ void CodeGenAction::ExecuteAction() {
       StringRef Msg = Err.getMessage();
       if (Msg.startswith("error: "))
         Msg = Msg.substr(7);
+
+      // Escape '%', which is interpreted as a format character.
+      llvm::SmallString<128> EscapedMessage;
+      for (unsigned i = 0, e = Msg.size(); i != e; ++i) {
+        if (Msg[i] == '%')
+          EscapedMessage += '%';
+        EscapedMessage += Msg[i];
+      }
+
       unsigned DiagID = CI.getDiagnostics().getCustomDiagID(
-          DiagnosticsEngine::Error, Msg);
+          DiagnosticsEngine::Error, EscapedMessage);
 
       CI.getDiagnostics().Report(Loc, DiagID);
       return;
diff --git a/clang/test/Frontend/ir-support-errors.ll b/clang/test/Frontend/ir-support-errors.ll
index 98227d46f7ae..cb5913cd3af8 100644
--- a/clang/test/Frontend/ir-support-errors.ll
+++ b/clang/test/Frontend/ir-support-errors.ll
@@ -3,6 +3,6 @@
 target triple = "x86_64-apple-darwin10"
 
 define i32 @f0() nounwind ssp {
-; CHECK: {{.*}}ir-support-errors.ll:7:16: error: expected value token
-       ret i32 x
+; CHECK: {{.*}}ir-support-errors.ll:7:16: error: use of undefined value '%x'
+       ret i32 %x
 }