diff --git a/lib/Sema/SemaExprObjC.cpp b/lib/Sema/SemaExprObjC.cpp
index 598ad0b..a3fe7d3 100644
--- a/lib/Sema/SemaExprObjC.cpp
+++ b/lib/Sema/SemaExprObjC.cpp
@@ -1379,10 +1379,12 @@
     ObjCMethodDecl *Method = ME->getMethodDecl();
     if (Method && Method->isSynthesized()) {
       Selector Sel = Method->getSelector();
-      if (Sel.getNumArgs() == 0)
+      if (Sel.getNumArgs() == 0) {
+        const DeclContext *Container = Method->getDeclContext();
         PDecl = 
-          S.LookupPropertyDecl(Method->getClassInterface(), 
+          S.LookupPropertyDecl(cast<ObjCContainerDecl>(Container),
                                Sel.getIdentifierInfoForSlot(0));
+      }
       if (PDecl)
         T = PDecl->getType();
     }
diff --git a/test/SemaObjC/weak-receiver-warn.m b/test/SemaObjC/weak-receiver-warn.m
index 56d9bc1..e6f8eab 100644
--- a/test/SemaObjC/weak-receiver-warn.m
+++ b/test/SemaObjC/weak-receiver-warn.m
@@ -66,3 +66,15 @@
 }
 
 @end
+
+
+// Weak properties on protocols can be synthesized by an adopting class.
+@protocol MyProtocol
+@property (weak) id object; // expected-note 2 {{property declared here}}
+@end
+
+void testProtocol(id <MyProtocol> input) {
+  [[input object] Meth]; // expected-warning {{weak property may be unpredictably null in ARC mode}}
+  [input.object Meth]; // expected-warning {{weak property may be unpredictably null in ARC mode}}
+}
+