Index: include/clang/AST/ASTImporter.h
===================================================================
--- include/clang/AST/ASTImporter.h
+++ include/clang/AST/ASTImporter.h
@@ -198,7 +198,7 @@
     /// Return the copy of the given declaration in the "to" context if
     /// it has already been imported from the "from" context.  Otherwise return
     /// NULL.
-    Decl *GetAlreadyImportedOrNull(Decl *FromD);
+    Decl *GetAlreadyImportedOrNull(const Decl *FromD) const;
 
     /// Import the given declaration context from the "from"
     /// AST context into the "to" AST context.
Index: lib/AST/ASTImporter.cpp
===================================================================
--- lib/AST/ASTImporter.cpp
+++ lib/AST/ASTImporter.cpp
@@ -1580,6 +1580,9 @@
     return Err;
 
   ToD = cast_or_null<NamedDecl>(Importer.GetAlreadyImportedOrNull(D));
+  if (ToD)
+    if (Error Err = ASTNodeImporter(*this).ImportDefinitionIfNeeded(D, ToD))
+      return Err;
 
   return Error::success();
 }
@@ -7729,17 +7732,12 @@
   return ToAttr;
 }
 
-Decl *ASTImporter::GetAlreadyImportedOrNull(Decl *FromD) {
-  llvm::DenseMap<Decl *, Decl *>::iterator Pos = ImportedDecls.find(FromD);
-  if (Pos != ImportedDecls.end()) {
-    Decl *ToD = Pos->second;
-    // FIXME: move this call to ImportDeclParts().
-    if (Error Err = ASTNodeImporter(*this).ImportDefinitionIfNeeded(FromD, ToD))
-      llvm::consumeError(std::move(Err));
-    return ToD;
-  } else {
+Decl *ASTImporter::GetAlreadyImportedOrNull(const Decl *FromD) const {
+  auto Pos = ImportedDecls.find(FromD);
+  if (Pos != ImportedDecls.end())
+    return Pos->second;
+  else
     return nullptr;
-  }
 }
 
 Decl *ASTImporter::Import(Decl *FromD) {