diff --git a/src/common/cpu/ZilogZ80.ts b/src/common/cpu/ZilogZ80.ts
index 648753ec..f15ce40d 100644
--- a/src/common/cpu/ZilogZ80.ts
+++ b/src/common/cpu/ZilogZ80.ts
@@ -1125,7 +1125,7 @@ let do_ix_add = function(operand)
    flags.H = (((ix & 0xfff) + (operand & 0xfff)) & 0x1000) ? 1 : 0;
    update_xy_flags((result & 0xff00) >>> 8);
    
-   ix = result;
+   ix = result & 0xffff;
 };