Index: kernel/generic/include/ddi/irq.h
===================================================================
--- kernel/generic/include/ddi/irq.h	(revision 228e490270cec3d6a6de666f61839f0d9ed5f193)
+++ kernel/generic/include/ddi/irq.h	(revision 1ab08524c23faeb2bd5c47b44081db505d503f9e)
@@ -189,4 +189,6 @@
 extern hash_table_t irq_uspace_hash_table;
 
+extern inr_t last_inr;
+
 extern void irq_init(size_t, size_t);
 extern void irq_initialize(irq_t *);
Index: kernel/generic/src/ddi/irq.c
===================================================================
--- kernel/generic/src/ddi/irq.c	(revision 228e490270cec3d6a6de666f61839f0d9ed5f193)
+++ kernel/generic/src/ddi/irq.c	(revision 1ab08524c23faeb2bd5c47b44081db505d503f9e)
@@ -136,4 +136,7 @@
 static size_t buckets;
 
+/** Last valid INR. */
+inr_t last_inr = 0;
+
 /** Initialize IRQ subsystem.
  *
@@ -145,4 +148,6 @@
 {
 	buckets = chains;
+	last_inr = inrs - 1;
+
 	/*
 	 * Be smart about the choice of the hash table operations.
Index: kernel/generic/src/ipc/irq.c
===================================================================
--- kernel/generic/src/ipc/irq.c	(revision 228e490270cec3d6a6de666f61839f0d9ed5f193)
+++ kernel/generic/src/ipc/irq.c	(revision 1ab08524c23faeb2bd5c47b44081db505d503f9e)
@@ -131,12 +131,11 @@
 /** Register an answerbox as a receiving end for IRQ notifications.
  *
- * @param box     Receiving answerbox.
- * @param inr     IRQ number.
- * @param devno   Device number.
- * @param imethod Interface and method to be associated
- *                with the notification.
- * @param ucode   Uspace pointer to top-half pseudocode.
- *
- * @return EBADMEM, ENOENT or EEXISTS on failure or 0 on success.
+ * @param box		Receiving answerbox.
+ * @param inr		IRQ number.
+ * @param devno		Device number.
+ * @param imethod	Interface and method to be associated with the
+ *			notification.
+ * @param ucode		Uspace pointer to top-half pseudocode.
+ * @return		EOK on success or a negative error code.
  *
  */
@@ -148,4 +147,7 @@
 		(sysarg_t) devno
 	};
+
+	if ((inr < 0) || (inr > last_inr))
+		return ELIMIT;
 	
 	irq_code_t *code;
@@ -208,8 +210,8 @@
 /** Unregister task from IRQ notification.
  *
- * @param box   Answerbox associated with the notification.
- * @param inr   IRQ number.
- * @param devno Device number.
- *
+ * @param box		Answerbox associated with the notification.
+ * @param inr		IRQ number.
+ * @param devno		Device number.
+ * @return		EOK on success or a negative error code.
  */
 int ipc_irq_unregister(answerbox_t *box, inr_t inr, devno_t devno)
@@ -219,4 +221,7 @@
 		(sysarg_t) devno
 	};
+
+	if ((inr < 0) || (inr > last_inr))
+		return ELIMIT;
 	
 	irq_spinlock_lock(&irq_uspace_hash_table_lock, true);