diff --git a/mandel.s b/mandel.s
index 9d3a2a6..df80ed7 100644
--- a/mandel.s
+++ b/mandel.s
@@ -584,6 +584,9 @@ point:
     ; pixel_mask <<= pixel_shift (shifting in ones)
     and #3
     sta pixel_shift
+    lda #3
+    sec
+    sbc pixel_shift
     tax
 shift_loop:
     beq shift_done