Index: COFF/InputFiles.cpp
===================================================================
--- COFF/InputFiles.cpp
+++ COFF/InputFiles.cpp
@@ -497,10 +497,9 @@
   if (!File)
     return "<internal>";
   if (File->ParentName.empty())
-    return File->getName().lower();
+    return File->getName();
 
-  std::string Res =
-      (getBasename(File->ParentName) + "(" + getBasename(File->getName()) + ")")
-          .str();
-  return StringRef(Res).lower();
+  return (getBasename(File->ParentName) + "(" + getBasename(File->getName()) +
+          ")")
+      .str();
 }
Index: test/COFF/filename-casing.s
===================================================================
--- test/COFF/filename-casing.s
+++ test/COFF/filename-casing.s
@@ -0,0 +1,14 @@
+# REQUIRES: x86
+
+# RUN: llvm-mc -filetype=obj -triple=x86_64-windows-msvc -o %T/MixedCase.obj %s
+# RUN: not lld-link /entry:main %T/MixedCase.obj 2>&1 | FileCheck -check-prefix=OBJECT %s
+
+# RUN: llvm-lib /out:%T/MixedCase.lib %T/MixedCase.obj
+# RUN: not lld-link /machine:x64 /entry:main %T/MixedCase.lib 2>&1 | FileCheck -check-prefix=ARCHIVE %s
+
+# OBJECT: MixedCase.obj: undefined symbol: f
+# ARCHIVE: MixedCase.lib(MixedCase.obj): undefined symbol: f
+
+.globl main
+main:
+	callq	f