diff --git a/extra/alien/data/map/map-tests.factor b/extra/alien/data/map/map-tests.factor
index e6845d1847..eb47d3675c 100644
--- a/extra/alien/data/map/map-tests.factor
+++ b/extra/alien/data/map/map-tests.factor
@@ -92,9 +92,11 @@ IN: alien.data.map.tests
 : vmerge-transpose ( a b c d -- ac bd ac bd )
     [ (vmerge) ] bi-curry@ bi* ; inline
 
+CONSTANT: plane-count 4
+
 : fold-rgba-planes ( r g b a -- rgba )
     [ vmerge-transpose vmerge-transpose ]
-    data-map( uchar-16 uchar-16 uchar-16 uchar-16 -- uchar-16[4] ) ;
+    data-map( uchar-16 uchar-16 uchar-16 uchar-16 -- uchar-16[plane-count] ) ;
 
 [
     B{
diff --git a/extra/alien/data/map/map.factor b/extra/alien/data/map/map.factor
index d4c24ef18f..48fcbcd97b 100644
--- a/extra/alien/data/map/map.factor
+++ b/extra/alien/data/map/map.factor
@@ -2,6 +2,7 @@
 USING: accessors alien alien.c-types alien.data alien.parser arrays
 byte-arrays combinators effects.parser fry generalizations kernel
 lexer locals macros make math math.ranges parser sequences sequences.private ;
+FROM: alien.arrays => array-length ;
 IN: alien.data.map
 
 ERROR: bad-data-map-input-length byte-length iter-size remainder ;
@@ -36,7 +37,7 @@ M: data-map-param nth-unsafe
 INSTANCE: data-map-param immutable-sequence
 
 : c-type-count ( in/out -- c-type count iter-length )
-    dup array? [ unclip swap product >fixnum ] [ 1 ] if
+    dup array? [ unclip swap array-length >fixnum ] [ 1 ] if
     2dup swap heap-size * >fixnum ; inline
 
 MACRO: >param ( in -- quot: ( array -- param ) )