Index: lib/Sema/SemaExprObjC.cpp
===================================================================
--- lib/Sema/SemaExprObjC.cpp
+++ lib/Sema/SemaExprObjC.cpp
@@ -2805,8 +2805,8 @@
       } else {
         if (ObjCMethodDecl *CurMeth = getCurMethodDecl()) {
           if (ObjCInterfaceDecl *ClassDecl = CurMeth->getClassInterface()) {
-            // FIXME: Is this correct? Why are we assuming that a message to
-            // Class will call a method in the current interface?
+            // As a guess, try looking for the method in the current interface.
+            // This very well may not produce the "right" method.
 
             // First check the public methods in the class interface.
             Method = ClassDecl->lookupClassMethod(Sel);
@@ -2814,8 +2814,7 @@
             if (!Method)
               Method = ClassDecl->lookupPrivateClassMethod(Sel);
 
-            if (Method && DiagnoseUseOfDecl(Method, SelectorSlotLocs, nullptr,
-                                            false, false, ClassDecl))
+            if (Method && DiagnoseUseOfDecl(Method, SelectorSlotLocs))
               return ExprError();
           }
         }
Index: test/SemaObjC/infer-availability-from-init.m
===================================================================
--- test/SemaObjC/infer-availability-from-init.m
+++ test/SemaObjC/infer-availability-from-init.m
@@ -56,3 +56,16 @@
   [self new];
 }
 @end
+
+@interface NoInit : NSObject
+-(instancetype)init __attribute__((unavailable)); // expected-note {{'init' has been explicitly marked unavailable here}}
+@end
+
+@interface NoInitSub : NoInit @end
+
+@implementation NoInitSub
+-(void)meth:(Class)c {
+  [c new]; // No error; unknown interface.
+  [NoInitSub new]; // expected-error {{'new' is unavailable}}
+}
+@end