diff --git a/kernel/irq/generic-chip.c b/kernel/irq/generic-chip.c
index 8743d62..95575d8 100644
--- a/kernel/irq/generic-chip.c
+++ b/kernel/irq/generic-chip.c
@@ -359,6 +359,9 @@
 
 	idx = hw_irq % dgc->irqs_per_chip;
 
+	if (test_bit(idx, &gc->unused))
+		return -ENOTSUPP;
+
 	if (test_bit(idx, &gc->installed))
 		return -EBUSY;