Index: uspace/lib/c/generic/async/client.c
===================================================================
--- uspace/lib/c/generic/async/client.c	(revision 622e7c90371690351474d65883d372074a6be553)
+++ uspace/lib/c/generic/async/client.c	(revision f5a7773d5901d6c1a9f44513cab36e8cd4c71a6c)
@@ -1052,5 +1052,9 @@
 static void async_hangup_internal(cap_phone_handle_t phone)
 {
-	(void) ipc_hangup(phone);
+	errno_t rc;
+
+	rc = ipc_hangup(phone);
+	assert(rc == EOK);
+	(void) rc;
 }
 
@@ -1077,5 +1081,7 @@
 		list_remove(&exch->sess_link);
 		list_remove(&exch->global_link);
-		async_hangup_internal(exch->phone);
+		if (sess->mgmt != EXCHANGE_ATOMIC &&
+		    sess->mgmt != EXCHANGE_SERIALIZE)
+			async_hangup_internal(exch->phone);
 		free(exch);
 	}