Index: COFF/Config.h
===================================================================
--- COFF/Config.h
+++ COFF/Config.h
@@ -115,7 +115,7 @@
   // Symbols in this set are considered as live by the garbage collector.
   std::vector<Symbol *> GCRoot;
 
-  std::set<StringRef> NoDefaultLibs;
+  std::set<std::string> NoDefaultLibs;
   bool NoDefaultLibAll = false;
 
   // True if we are creating a DLL.
Index: COFF/Driver.cpp
===================================================================
--- COFF/Driver.cpp
+++ COFF/Driver.cpp
@@ -296,6 +296,17 @@
          (!Config->MinGW && Sym.contains('@'));
 }
 
+// The casing of the libraries path stamped in the OBJ can differ from the
+// actual path on disk. With this, we ensure to always use lowercase as a key
+// and for comparisons, at least on Windows.
+static std::string normalizeLibPath(StringRef path) {
+#if defined(_WIN32)
+  return path.lower();
+#else // LINUX
+  return path;
+#endif
+}
+
 // Parses .drectve section contents and returns a list of files
 // specified by /defaultlib.
 void LinkerDriver::parseDirectives(InputFile *File) {
@@ -356,7 +367,8 @@
       parseMerge(Arg->getValue());
       break;
     case OPT_nodefaultlib:
-      Config->NoDefaultLibs.insert(doFindLib(Arg->getValue()));
+      Config->NoDefaultLibs.insert(
+          normalizeLibPath(doFindLib(Arg->getValue())));
       break;
     case OPT_section:
       parseSection(Arg->getValue());
@@ -457,7 +469,7 @@
     return None;
 
   StringRef Path = doFindLib(Filename);
-  if (Config->NoDefaultLibs.count(Path))
+  if (Config->NoDefaultLibs.count(normalizeLibPath(Path)))
     return None;
 
   if (Optional<sys::fs::UniqueID> ID = getUniqueID(Path))
@@ -1240,7 +1252,7 @@
 
   // Handle /nodefaultlib:<filename>
   for (auto *Arg : Args.filtered(OPT_nodefaultlib))
-    Config->NoDefaultLibs.insert(doFindLib(Arg->getValue()));
+    Config->NoDefaultLibs.insert(normalizeLibPath(doFindLib(Arg->getValue())));
 
   // Handle /nodefaultlib
   if (Args.hasArg(OPT_nodefaultlib_all))
Index: test/COFF/nodefaultlib.test
===================================================================
--- test/COFF/nodefaultlib.test
+++ test/COFF/nodefaultlib.test
@@ -29,3 +29,10 @@
 
 # RUN: env LIB=%T lld-link /out:%t.exe /entry:main \
 # RUN:   /subsystem:console hello64.obj /defaultlib:std64.lib
+
+MSVC stamps uppercase references in OBJ directives, thus ensure that passing lowercase 'libcmt' and 'oldnames' to /nodefaultlib works.
+# RUN: lld-link %S/Inputs/precomp.obj %S/Inputs/precomp-a.obj %S/Inputs/precomp-b.obj /nodefaultlib:libcmt /nodefaultlib:oldnames /entry:main /debug /pdb:%t.pdb /out:%t.exe /opt:ref /opt:icf
+# RUN: llvm-pdbutil dump -types %t.pdb | FileCheck %s -check-prefix UPPERCASE
+
+UPPERCASE-NOT: OLDNAMES
+UPPERCASE-NOT: LIBCMT
\ No newline at end of file