Index: kernel/generic/src/ipc/ipc.c
===================================================================
--- kernel/generic/src/ipc/ipc.c	(revision 9f8a9627dfaf96b77308c647b78334cc3bfc71ee)
+++ kernel/generic/src/ipc/ipc.c	(revision 5b7e17ea3b5aab2cca5a52544f7687c5365b3d75)
@@ -351,5 +351,8 @@
 	} else {
 		atomic_inc(&phone->active_calls);
-		atomic_inc(&caller->answerbox.active_calls);
+		if (call->callerbox)
+			atomic_inc(&call->callerbox->active_calls);
+		else
+			atomic_inc(&caller->answerbox.active_calls);
 		kobject_add_ref(phone->kobject);
 		call->sender = caller;