Index: uspace/lib/hound/src/protocol.c
===================================================================
--- uspace/lib/hound/src/protocol.c	(revision beb83c14fc69926ddb40d44bb96dc734b5d21545)
+++ uspace/lib/hound/src/protocol.c	(revision c483fca0263f4b26f181c7f35c6de491be6e53d5)
@@ -615,5 +615,12 @@
 			break;
 		default:
-			async_answer_0(&call, ENOTSUP);
+			/*
+			 * In case we called async_get_call() after we had
+			 * already received IPC_M_PHONE_HUNGUP deeper in the
+			 * protocol handling, the capability handle will be
+			 * invalid, so act carefully here.
+			 */
+			if (call.cap_handle != CAP_NIL)
+				async_answer_0(&call, ENOTSUP);
 			return;
 		}