diff --git a/clang/lib/Sema/SemaDeclAttr.cpp b/clang/lib/Sema/SemaDeclAttr.cpp
--- a/clang/lib/Sema/SemaDeclAttr.cpp
+++ b/clang/lib/Sema/SemaDeclAttr.cpp
@@ -3389,7 +3389,8 @@
   }
   Ty = getFunctionOrMethodResultType(D);
   // replace instancetype with the class type
-  if (Ty.getTypePtr() == S.Context.getObjCInstanceTypeDecl()->getTypeForDecl())
+  auto Instancetype = S.Context.getObjCInstanceTypeDecl()->getTypeForDecl();
+  if (Ty->getAs<TypedefType>() == Instancetype)
     if (auto *OMD = dyn_cast<ObjCMethodDecl>(D))
       if (auto *Interface = OMD->getClassInterface())
         Ty = S.Context.getObjCObjectPointerType(
diff --git a/clang/test/SemaObjC/format-arg-attribute.m b/clang/test/SemaObjC/format-arg-attribute.m
--- a/clang/test/SemaObjC/format-arg-attribute.m
+++ b/clang/test/SemaObjC/format-arg-attribute.m
@@ -2,7 +2,10 @@
 
 @interface NSString
 +(instancetype)stringWithCString:(const char *)cstr __attribute__((format_arg(1)));
-+(instancetype)stringWithString:(NSString *)cstr __attribute__((format_arg(1)));
+-(instancetype)initWithString:(NSString *)str __attribute__((format_arg(1)));
+
++(instancetype _Nonnull)nonNullableString:(NSString *)str __attribute__((format_arg(1)));
++(instancetype _Nullable)nullableString:(NSString *)str __attribute__((format_arg(1)));
 @end
 
 @protocol MaybeString