Index: kernel/generic/include/ipc/ipc.h
===================================================================
--- kernel/generic/include/ipc/ipc.h	(revision 75b139ff9b51040615599b12a162dab865b3faac)
+++ kernel/generic/include/ipc/ipc.h	(revision 6d351e674a67b6ecee3c205c0f09e29e92b462be)
@@ -147,4 +147,11 @@
 	struct task *sender;
 	
+	/*
+	 * Answerbox that will receive the answer.
+	 * This will most of the times be the sender's answerbox,
+	 * but we allow for useful exceptions.
+	 */
+	answerbox_t *callerbox;
+
 	/** Phone which was used to send the call. */
 	phone_t *caller_phone;