--- src/kernel/sel4/src/plat/pc99/machine/ioapic.c
+++ src/kernel/sel4/src/plat/pc99/machine/ioapic.c
@@ -127,6 +127,9 @@ void ioapic_mask(bool_t mask, uint32_t ioapic, uint32_t pin)
         return;
     }
     if (mask) {
+        /* only mask level triggered interrupts */
+        if (!(ioredtbl_state[index] & IOREDTBL_LOW_TRIGGER_MODE_LEVEL)) 
+            return;
         ioredtbl_state[index] |= IOREDTBL_LOW_INTERRUPT_MASK;
     } else {
         ioredtbl_state[index] &= ~IOREDTBL_LOW_INTERRUPT_MASK;