Index: llvm/trunk/include/llvm/Support/Error.h
===================================================================
--- llvm/trunk/include/llvm/Support/Error.h
+++ llvm/trunk/include/llvm/Support/Error.h
@@ -322,7 +322,7 @@
 /// Subclass of Error for the sole purpose of identifying the success path in
 /// the type system. This allows to catch invalid conversion to Expected<T> at
 /// compile time.
-class ErrorSuccess : public Error {};
+class ErrorSuccess final : public Error {};
 
 inline ErrorSuccess Error::success() { return ErrorSuccess(); }
 
@@ -1171,8 +1171,7 @@
 /// show more detailed information to the user.
 class FileError final : public ErrorInfo<FileError> {
 
-  template <class Err>
-  friend Error createFileError(std::string, Err);
+  friend Error createFileError(std::string, Error);
 
 public:
   void log(raw_ostream &OS) const override {
@@ -1207,11 +1206,12 @@
 
 /// Concatenate a source file path and/or name with an Error. The resulting
 /// Error is unchecked.
-template <class Err>
-inline Error createFileError(std::string F, Err E) {
+inline Error createFileError(std::string F, Error E) {
   return FileError::build(F, std::move(E));
 }
 
+Error createFileError(std::string F, ErrorSuccess) = delete;
+
 /// Helper for check-and-exit error handling.
 ///
 /// For tool use only. NOT FOR USE IN LIBRARY CODE.
Index: llvm/trunk/unittests/Support/ErrorTest.cpp
===================================================================
--- llvm/trunk/unittests/Support/ErrorTest.cpp
+++ llvm/trunk/unittests/Support/ErrorTest.cpp
@@ -874,6 +874,9 @@
       },
       "");
 #endif
+  // Not allowed, would fail at compile-time
+  //consumeError(createFileError("file.bin", ErrorSuccess()));
+
   Error E1 = make_error<CustomError>(1);
   Error FE1 = createFileError("file.bin", std::move(E1));
   EXPECT_EQ(toString(std::move(FE1)).compare("'file.bin': CustomError {1}"), 0);