diff --git a/extra/noise/noise-tests.factor b/extra/noise/noise-tests.factor
new file mode 100644
index 0000000000..e216637c51
--- /dev/null
+++ b/extra/noise/noise-tests.factor
@@ -0,0 +1,4 @@
+IN: noise.tests
+USING: noise tools.test sequences math ;
+
+[ t ] [ { 100 100 } perlin-noise-map-coords [ [ 100 <= ] all? ] all? ] unit-test
diff --git a/extra/noise/noise.factor b/extra/noise/noise.factor
index a27cc186a0..9204fa55f1 100644
--- a/extra/noise/noise.factor
+++ b/extra/noise/noise.factor
@@ -120,7 +120,7 @@ TYPED:: perlin-noise ( table: byte-array point: float-4 -- value: float )
     faded trilerp ;
 
 MEMO: perlin-noise-map-coords ( dim -- coords )
-    first2 [| x y | x [ y 0.0 0.0 float-4-boa ] float-4-array{ } map-as ] with map concat ; 
+    first2 iota [| x y | x iota [ y 0.0 0.0 float-4-boa ] float-4-array{ } map-as ] with map concat ;
 
 TYPED:: perlin-noise-map ( table: byte-array transform: matrix4 coords: float-4-array -- map: float-array )
     coords [| coord | table transform coord m4.v perlin-noise ] data-map( float-4 -- c:float )