Index: cfe/trunk/lib/StaticAnalyzer/Checkers/ObjCPropertyChecker.cpp
===================================================================
--- cfe/trunk/lib/StaticAnalyzer/Checkers/ObjCPropertyChecker.cpp
+++ cfe/trunk/lib/StaticAnalyzer/Checkers/ObjCPropertyChecker.cpp
@@ -58,8 +58,7 @@
   if (const ObjCInterfaceDecl *IntD =
           dyn_cast<ObjCInterfaceDecl>(D->getDeclContext())) {
     ImplD = IntD->getImplementation();
-  } else {
-    const ObjCCategoryDecl *CatD = cast<ObjCCategoryDecl>(D->getDeclContext());
+  } else if (auto *CatD = dyn_cast<ObjCCategoryDecl>(D->getDeclContext())) {
     ImplD = CatD->getClassInterface()->getImplementation();
   }
 
Index: cfe/trunk/test/Analysis/ObjCPropertiesSyntaxChecks.m
===================================================================
--- cfe/trunk/test/Analysis/ObjCPropertiesSyntaxChecks.m
+++ cfe/trunk/test/Analysis/ObjCPropertiesSyntaxChecks.m
@@ -59,3 +59,10 @@
 @interface IWithoutImpl : NSObject {}
 @property(copy) NSMutableString *mutableStr; // no-warning
 @end
+
+@protocol SomeProtocol
+// Don't warn on protocol properties because it is possible to
+// conform to them correctly; it is only synthesized setters that
+// that are definitely incorrect.
+@property (copy) NSMutableString *myProp; // no-crash // no-warning
+@end