Index: kernel/generic/src/ipc/ipc.c
===================================================================
--- kernel/generic/src/ipc/ipc.c	(revision aadde10132deef35da3c7242badf46fedcfdd564)
+++ kernel/generic/src/ipc/ipc.c	(revision 3212921a1eccd711a490caff49e430b6d9502188)
@@ -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;