diff --git a/include/swift/AST/ASTContext.h b/include/swift/AST/ASTContext.h
index a43f36df646..050449e66f3 100644
--- a/include/swift/AST/ASTContext.h
+++ b/include/swift/AST/ASTContext.h
@@ -183,9 +183,6 @@ public:
   /// This state should be tracked somewhere else.
   unsigned LastCheckedExternalDefinition = 0;
 
-  /// \brief The list of externally-created types that need validation.
-  std::vector<Type> ExternalTypes;
-
 private:
   /// \brief The current generation number, which reflects the number of
   /// times that external modules have been loaded.
@@ -336,10 +333,6 @@ public:
   /// was just added.
   void addedExternalDecl(Decl *decl);
 
-  /// \brief Notify all of the mutation listeners that the given type
-  /// was just added.
-  void addedExternalType(Type type);
-
   /// Add a cleanup function to be called when the ASTContext is deallocated.
   void addCleanup(std::function<void(void)> cleanup);
 
diff --git a/include/swift/AST/ASTMutationListener.h b/include/swift/AST/ASTMutationListener.h
index f856bb6fb5b..ae9b3af3cb7 100644
--- a/include/swift/AST/ASTMutationListener.h
+++ b/include/swift/AST/ASTMutationListener.h
@@ -27,9 +27,6 @@ namespace swift {
 
     /// \brief A new declaration was added to the AST.
     virtual void addedExternalDecl(Decl *decl) = 0;
-
-    /// \brief A new type was added to the AST.
-    virtual void addedExternalType(Type type) = 0;
   };
 }
 
diff --git a/lib/AST/ASTContext.cpp b/lib/AST/ASTContext.cpp
index ab38f47da32..c78f66b85b5 100644
--- a/lib/AST/ASTContext.cpp
+++ b/lib/AST/ASTContext.cpp
@@ -541,11 +541,6 @@ void ASTContext::addedExternalDecl(Decl *decl) {
     listener->addedExternalDecl(decl);
 }
 
-void ASTContext::addedExternalType(Type type) {
-  for (auto listener : Impl.MutationListeners)
-    listener->addedExternalType(type);
-}
-
 void ASTContext::addCleanup(std::function<void(void)> cleanup) {
   Impl.Cleanups.push_back(std::move(cleanup));
 }
diff --git a/lib/ClangImporter/ImportType.cpp b/lib/ClangImporter/ImportType.cpp
index f0b85a4780a..6bd05afa602 100644
--- a/lib/ClangImporter/ImportType.cpp
+++ b/lib/ClangImporter/ImportType.cpp
@@ -560,10 +560,7 @@ Type ClangImporter::Implementation::importType(clang::QualType type,
   }
   
   SwiftTypeConverter converter(*this, kind);
-  Type converted = converter.Visit(type.getTypePtr());
-  if (converted)
-    SwiftContext.addedExternalType(converted);
-  return converted;
+  return converter.Visit(type.getTypePtr());
 }
 
 /// Given the first selector piece for an init method, e.g., \c initWithFoo,
diff --git a/lib/Sema/NameBinding.cpp b/lib/Sema/NameBinding.cpp
index 2983ab58857..2e4942315e8 100644
--- a/lib/Sema/NameBinding.cpp
+++ b/lib/Sema/NameBinding.cpp
@@ -332,11 +332,6 @@ namespace {
     virtual void addedExternalDecl(Decl *decl) {
       TU->getASTContext().ExternalDefinitions.insert(decl);
     }
-
-    /// \brief A new type was added to the AST.
-    virtual void addedExternalType(Type type) {
-      TU->getASTContext().ExternalTypes.push_back(type);
-    }
 };
 }
 
diff --git a/lib/Sema/TypeChecker.cpp b/lib/Sema/TypeChecker.cpp
index 632c5f006e5..c52f136e617 100644
--- a/lib/Sema/TypeChecker.cpp
+++ b/lib/Sema/TypeChecker.cpp
@@ -62,10 +62,6 @@ void TypeChecker::addedExternalDecl(Decl *decl) {
   Context.ExternalDefinitions.insert(decl);
 }
 
-void TypeChecker::addedExternalType(Type type) {
-  Context.ExternalTypes.push_back(type);
-}
-
 ProtocolDecl *TypeChecker::getProtocol(SourceLoc loc, KnownProtocolKind kind) {
   auto protocol = Context.getProtocol(kind);
   if (!protocol && loc.isValid()) {
diff --git a/lib/Sema/TypeChecker.h b/lib/Sema/TypeChecker.h
index 09ce46c9a80..5c3f47ec505 100644
--- a/lib/Sema/TypeChecker.h
+++ b/lib/Sema/TypeChecker.h
@@ -705,10 +705,6 @@ public:
 
   /// \brief A new declaration was added to the AST.
   virtual void addedExternalDecl(Decl *decl);
-
-  /// \brief A new type was added to the AST.
-  virtual void addedExternalType(Type type);
-
   /// @}
 
   /// \name Lazy resolution.