Index: clang/include/clang/Lex/Preprocessor.h
===================================================================
--- clang/include/clang/Lex/Preprocessor.h
+++ clang/include/clang/Lex/Preprocessor.h
@@ -2242,11 +2242,11 @@
   };
 
   Optional<FileEntryRef> LookupHeaderIncludeOrImport(
-      const DirectoryLookup *&CurDir, StringRef Filename,
+      const DirectoryLookup *&CurDir, StringRef &Filename,
       SourceLocation FilenameLoc, CharSourceRange FilenameRange,
       const Token &FilenameTok, bool &IsFrameworkFound, bool IsImportDecl,
       bool &IsMapped, const DirectoryLookup *LookupFrom,
-      const FileEntry *LookupFromFile, StringRef LookupFilename,
+      const FileEntry *LookupFromFile, StringRef &LookupFilename,
       SmallVectorImpl<char> &RelativePath, SmallVectorImpl<char> &SearchPath,
       ModuleMap::KnownHeader &SuggestedModule, bool isAngled);
 
Index: clang/lib/Lex/PPDirectives.cpp
===================================================================
--- clang/lib/Lex/PPDirectives.cpp
+++ clang/lib/Lex/PPDirectives.cpp
@@ -1716,11 +1716,11 @@
 }
 
 Optional<FileEntryRef> Preprocessor::LookupHeaderIncludeOrImport(
-    const DirectoryLookup *&CurDir, StringRef Filename,
+    const DirectoryLookup *&CurDir, StringRef& Filename,
     SourceLocation FilenameLoc, CharSourceRange FilenameRange,
     const Token &FilenameTok, bool &IsFrameworkFound, bool IsImportDecl,
     bool &IsMapped, const DirectoryLookup *LookupFrom,
-    const FileEntry *LookupFromFile, StringRef LookupFilename,
+    const FileEntry *LookupFromFile, StringRef& LookupFilename,
     SmallVectorImpl<char> &RelativePath, SmallVectorImpl<char> &SearchPath,
     ModuleMap::KnownHeader &SuggestedModule, bool isAngled) {
   Optional<FileEntryRef> File = LookupFile(
@@ -1789,21 +1789,10 @@
       return Filename;
     };
     StringRef TypoCorrectionName = CorrectTypoFilename(Filename);
-
-#ifndef _WIN32
-    // Normalize slashes when compiling with -fms-extensions on non-Windows.
-    // This is unnecessary on Windows since the filesystem there handles
-    // backslashes.
-    SmallString<128> NormalizedTypoCorrectionPath;
-    if (LangOpts.MicrosoftExt) {
-      NormalizedTypoCorrectionPath = TypoCorrectionName;
-      llvm::sys::path::native(NormalizedTypoCorrectionPath);
-      TypoCorrectionName = NormalizedTypoCorrectionPath;
-    }
-#endif
+    StringRef TypoCorrectionLookupName = CorrectTypoFilename(LookupFilename);
 
     Optional<FileEntryRef> File = LookupFile(
-        FilenameLoc, TypoCorrectionName, isAngled, LookupFrom, LookupFromFile,
+        FilenameLoc, TypoCorrectionLookupName, isAngled, LookupFrom, LookupFromFile,
         CurDir, Callbacks ? &SearchPath : nullptr,
         Callbacks ? &RelativePath : nullptr, &SuggestedModule, &IsMapped,
         /*IsFrameworkFound=*/nullptr);
@@ -1818,6 +1807,7 @@
       // We found the file, so set the Filename to the name after typo
       // correction.
       Filename = TypoCorrectionName;
+      LookupFilename = TypoCorrectionLookupName;
       return File;
     }
   }
@@ -2074,8 +2064,6 @@
   if (Callbacks && !IsImportDecl) {
     // Notify the callback object that we've seen an inclusion directive.
     // FIXME: Use a different callback for a pp-import?
-    // FIXME: Passes wrong filename if LookupHeaderIncludeOrImport() did
-    // typo correction.
     Callbacks->InclusionDirective(
         HashLoc, IncludeTok, LookupFilename, isAngled, FilenameRange,
         File ? &File->getFileEntry() : nullptr, SearchPath, RelativePath,
@@ -2102,7 +2090,6 @@
       !IsMapped && !File->getFileEntry().tryGetRealPathName().empty();
 
   if (CheckIncludePathPortability) {
-    // FIXME: Looks at the wrong filename if we did typo correction.
     StringRef Name = LookupFilename;
     StringRef NameWithoriginalSlashes = Filename;
 #if defined(_WIN32)
Index: clang/test/Lexer/case-insensitive-include-pr31836.sh
===================================================================
--- clang/test/Lexer/case-insensitive-include-pr31836.sh
+++ clang/test/Lexer/case-insensitive-include-pr31836.sh
@@ -2,7 +2,8 @@
 
 // RUN: mkdir -p %t
 // RUN: touch %t/case-insensitive-include-pr31836.h
-// RUN: echo "#include \"%t/Case-Insensitive-Include-Pr31836.h\"" | %clang_cc1 -E - 2>&1 | FileCheck %s
+// RUN: echo "#include \"\\\\\\\\?\\\\%t/Case-Insensitive-Include-Pr31836.h\"" | not %clang_cc1 -E - 2>&1 | FileCheck %s
 
+// CHECK: error: {{.*}}file not found, did you mean
 // CHECK: warning: non-portable path to file
 // CHECK-SAME: /case-insensitive-include-pr31836.h
Index: clang/test/Lexer/case-insensitive-include-win.c
===================================================================
--- clang/test/Lexer/case-insensitive-include-win.c
+++ clang/test/Lexer/case-insensitive-include-win.c
@@ -5,6 +5,6 @@
 // REQUIRES: system-windows
 // RUN: mkdir -p %t.dir
 // RUN: touch %t.dir/foo.h
-// RUN: not %clang_cl /FI\\?\%t.dir\FOO.h /WX -Xclang -verify -fsyntax-only %s 2>&1 | FileCheck %s
+// RUN: not %clang_cl /FI\\?\%t.dir\FOO.h /WX -fsyntax-only %s 2>&1 | FileCheck %s
 
 // CHECK: non-portable path to file '"\\?\