diff --git a/libsrc/runtime/lumod.s b/libsrc/runtime/lumod.s
index 526db7f10..00f5e7353 100644
--- a/libsrc/runtime/lumod.s
+++ b/libsrc/runtime/lumod.s
@@ -14,7 +14,7 @@ tosumodeax:
  	lda	tmp3		; Remainder is in ptr2:tmp3:tmp4
 	sta	sreg
 	lda	tmp4
-	sta	sreg
+	sta	sreg+1
 	lda	ptr2
 	ldx	ptr2+1
 	rts