diff --git a/mandel.s b/mandel.s
index 6977582..4ab6c19 100644
--- a/mandel.s
+++ b/mandel.s
@@ -1106,10 +1106,9 @@ cont:
 enough:
 .endmacro
 
-.macro zoom_factor dest, src, zoom, aspect
+.macro zoom_factor dest, src, aspect
     ; output: dest: fixed8.24
     ; input: src: fixed4.12
-    ; input: zoom: u8 ???
     ; aspect: fixed4.12
     ; clobbers A, X, flags, etc
     copy16 dest, src
@@ -1602,9 +1601,9 @@ skipped_mask:
 not_skipped_mask:
 
     ; run the fractal!
-    zoom_factor cx, sx, zoom, aspect_x
+    zoom_factor cx, sx, aspect_x
     add32 cx, cx, ox
-    zoom_factor cy, sy, zoom, aspect_y
+    zoom_factor cy, sy, aspect_y
     add32 cy, cy, oy
     jsr mandelbrot
     jsr pset