diff --git a/include/clang/Sema/ExternalSemaSource.h b/include/clang/Sema/ExternalSemaSource.h
index cbce757..901b444 100644
--- a/include/clang/Sema/ExternalSemaSource.h
+++ b/include/clang/Sema/ExternalSemaSource.h
@@ -14,6 +14,7 @@
 #define LLVM_CLANG_SEMA_EXTERNAL_SEMA_SOURCE_H
 
 #include "clang/AST/ExternalASTSource.h"
+#include "clang/Sema/TypoCorrection.h"
 #include "clang/Sema/Weak.h"
 #include "llvm/ADT/MapVector.h"
 #include <utility>
@@ -177,6 +178,22 @@ public:
                  SmallVectorImpl<std::pair<ValueDecl *, 
                                            SourceLocation> > &Pending) {}
 
+  /// \copydoc Sema::CorrectTypo
+  /// \note LookupKind must correspond to a valid Sema::LookupNameKind
+  ///
+  /// ExternalSemaSource::CorrectTypo is always given the first chance to
+  /// correct a typo (really, to offer suggestions to repair a failed lookup).
+  /// It will even be called when SpellChecking is turned off or after a
+  /// fatal error has already been detected.
+  TypoCorrection CorrectTypo(const DeclarationNameInfo &Typo,
+                             int LookupKind, Scope *S, CXXScopeSpec *SS,
+                             CorrectionCandidateCallback &CCC,
+                             DeclContext *MemberContext,
+                             bool EnteringContext,
+                             const ObjCObjectPointerType *OPT) {
+    return TypoCorrection();
+  }
+
   // isa/cast/dyn_cast support
   static bool classof(const ExternalASTSource *Source) {
     return Source->SemaSource;
diff --git a/include/clang/Sema/MultiplexExternalSemaSource.h b/include/clang/Sema/MultiplexExternalSemaSource.h
index ff87d05..f8521dc 100644
--- a/include/clang/Sema/MultiplexExternalSemaSource.h
+++ b/include/clang/Sema/MultiplexExternalSemaSource.h
@@ -322,6 +322,15 @@ public:
   virtual void ReadPendingInstantiations(
               SmallVectorImpl<std::pair<ValueDecl*, SourceLocation> >& Pending);
 
+  /// \copydoc ExternalSemaSource::CorrectTypo
+  /// \note Returns the first nonempty correction.
+  virtual TypoCorrection CorrectTypo(const DeclarationNameInfo &Typo,
+                                     int LookupKind, Scope *S, CXXScopeSpec *SS,
+                                     CorrectionCandidateCallback &CCC,
+                                     DeclContext *MemberContext,
+                                     bool EnteringContext,
+                                     const ObjCObjectPointerType *OPT);
+
   // isa/cast/dyn_cast support
   static bool classof(const MultiplexExternalSemaSource*) { return true; }
   //static bool classof(const ExternalSemaSource*) { return true; }
diff --git a/lib/Sema/MultiplexExternalSemaSource.cpp b/lib/Sema/MultiplexExternalSemaSource.cpp
index d85624b..3f391bf 100644
--- a/lib/Sema/MultiplexExternalSemaSource.cpp
+++ b/lib/Sema/MultiplexExternalSemaSource.cpp
@@ -267,3 +267,19 @@ void MultiplexExternalSemaSource::ReadPendingInstantiations(
   for(size_t i = 0; i < Sources.size(); ++i)
     Sources[i]->ReadPendingInstantiations(Pending);
 }
+
+TypoCorrection MultiplexExternalSemaSource::CorrectTypo(
+                                     const DeclarationNameInfo &Typo,
+                                     int LookupKind, Scope *S, CXXScopeSpec *SS,
+                                     CorrectionCandidateCallback &CCC,
+                                     DeclContext *MemberContext,
+                                     bool EnteringContext,
+                                     const ObjCObjectPointerType *OPT) {
+  for(size_t i = 0; i < Sources.size(); ++i) {
+    if (TypoCorrection c = Sources[i]->CorrectTypo(Typo, LookupKind, S, SS, CCC,
+                                                   MemberContext,
+                                                   EnteringContext, OPT))
+      return c;
+  }
+  return TypoCorrection();
+}
diff --git a/lib/Sema/SemaLookup.cpp b/lib/Sema/SemaLookup.cpp
index 8d954ca..fb71960 100644
--- a/lib/Sema/SemaLookup.cpp
+++ b/lib/Sema/SemaLookup.cpp
@@ -3779,6 +3779,14 @@ TypoCorrection Sema::CorrectTypo(const DeclarationNameInfo &TypoName,
                                  DeclContext *MemberContext,
                                  bool EnteringContext,
                                  const ObjCObjectPointerType *OPT) {
+  // Always let the ExternalSource have the first chance at correction, even
+  // if we would otherwise have given up.
+  if (ExternalSource) {
+    if (TypoCorrection Correction = ExternalSource->CorrectTypo(
+        TypoName, LookupKind, S, SS, CCC, MemberContext, EnteringContext, OPT))
+      return Correction;
+  }
+
   if (Diags.hasFatalErrorOccurred() || !getLangOpts().SpellChecking)
     return TypoCorrection();