diff --git a/zsnes/src/cpu/regs.inc b/zsnes/src/cpu/regs.inc
index 56bad46b..4c675fa2 100644
--- a/zsnes/src/cpu/regs.inc
+++ b/zsnes/src/cpu/regs.inc
@@ -1180,6 +1180,7 @@ reg4017r:
     ret
 
 reg4100r:
+   xor al,al
    cmp byte[nssdip1],1
    jne .nodip1
    mov al,1