Index: lib/Sema/SemaDeclAttr.cpp
===================================================================
--- lib/Sema/SemaDeclAttr.cpp
+++ lib/Sema/SemaDeclAttr.cpp
@@ -540,14 +540,13 @@
   // a DeclRefExpr is found, its type should be checked to determine whether it
   // is a capability or not.
 
-  if (const auto *E = dyn_cast<DeclRefExpr>(Ex))
-    return typeHasCapability(S, E->getType());
-  else if (const auto *E = dyn_cast<CastExpr>(Ex))
+  if (const auto *E = dyn_cast<CastExpr>(Ex))
     return isCapabilityExpr(S, E->getSubExpr());
   else if (const auto *E = dyn_cast<ParenExpr>(Ex))
     return isCapabilityExpr(S, E->getSubExpr());
   else if (const auto *E = dyn_cast<UnaryOperator>(Ex)) {
-    if (E->getOpcode() == UO_LNot)
+    if (E->getOpcode() == UO_LNot || E->getOpcode() == UO_AddrOf ||
+        E->getOpcode() == UO_Deref)
       return isCapabilityExpr(S, E->getSubExpr());
     return false;
   } else if (const auto *E = dyn_cast<BinaryOperator>(Ex)) {
@@ -557,7 +556,7 @@
     return false;
   }
 
-  return false;
+  return typeHasCapability(S, Ex->getType());
 }
 
 /// \brief Checks that all attribute arguments, starting from Sidx, resolve to
Index: test/Sema/attr-capabilities.cpp
===================================================================
--- /dev/null
+++ test/Sema/attr-capabilities.cpp
@@ -0,0 +1,17 @@
+// RUN: %clang_cc1 -fsyntax-only -Wthread-safety -verify %s
+
+class __attribute__((shared_capability("mutex"))) Mutex {
+ public:
+  void func1() __attribute__((assert_capability(this)));
+  void func2() __attribute__((assert_capability(!this)));
+
+  const Mutex& operator!() const { return *this; }
+};
+
+class NotACapability {
+ public:
+  void func1() __attribute__((assert_capability(this)));  // expected-warning {{'assert_capability' attribute requires arguments whose type is annotated with 'capability' attribute; type here is 'NotACapability *'}}
+  void func2() __attribute__((assert_capability(!this)));  // expected-warning {{'assert_capability' attribute requires arguments whose type is annotated with 'capability' attribute; type here is 'bool'}}
+
+  const NotACapability& operator!() const { return *this; }
+};
Index: test/SemaCXX/warn-thread-safety-parsing.cpp
===================================================================
--- test/SemaCXX/warn-thread-safety-parsing.cpp
+++ test/SemaCXX/warn-thread-safety-parsing.cpp
@@ -351,7 +351,8 @@
 int gb_var_arg_6 GUARDED_BY(muRef);
 int gb_var_arg_7 GUARDED_BY(muDoubleWrapper.getWrapper()->getMu());
 int gb_var_arg_8 GUARDED_BY(muPointer);
-
+int gb_var_arg_9 GUARDED_BY(!&mu1);
+int gb_var_arg_10 GUARDED_BY(!&*&mu1);
 
 // illegal attribute arguments
 int gb_var_arg_bad_1 GUARDED_BY(1); // \