diff --git a/libsrc/runtime/udiv.s b/libsrc/runtime/udiv.s
index 4dbc477aa..e667af0e2 100644
--- a/libsrc/runtime/udiv.s
+++ b/libsrc/runtime/udiv.s
@@ -34,7 +34,7 @@ tosudivax:
 udiv16:	lda	#0
  	sta	ptr1+1
  	ldy	#16
-        ldx     sreg+1
+        ldx     ptr4+1
         beq     udiv16by8a
 
 L0:	asl	sreg