diff --git a/Source/HBIOS/acia.asm b/Source/HBIOS/acia.asm
index 94402b1f..2e030a76 100644
--- a/Source/HBIOS/acia.asm
+++ b/Source/HBIOS/acia.asm
@@ -158,6 +158,17 @@ ACIA_INIT1:
 ;
 ; INTERRUPT HANDLERS
 ;
+#IF (INTMODE == 0)
+;
+; NO INTERRUPT HANDLERS UNDER INTMODE 0.  GENERATE A PANIC
+; IF SOMETHING TRIES TO CALL THEM.
+;
+ACIA0_INT:
+ACIA1_INT:
+	CALL	PANIC
+;
+#ENDIF
+;
 #IF (INTMODE > 0)
 ;
 ACIA0_INT: