diff --git a/basis/ui/pens/gradient/gradient-tests.factor b/basis/ui/pens/gradient/gradient-tests.factor
index 63134b3c8e..22802d39ae 100644
--- a/basis/ui/pens/gradient/gradient-tests.factor
+++ b/basis/ui/pens/gradient/gradient-tests.factor
@@ -1,4 +1,24 @@
-! Copyright (C) 2009 Slava Pestov.
-! See http://factorcode.org/license.txt for BSD license.
-USING: tools.test ui.pens.gradient ;
+USING: tools.test ui.pens.gradient ui.pens.gradient.private
+colors.constants specialized-arrays alien.c-types ;
+SPECIALIZED-ARRAY: float
 IN: ui.pens.gradient.tests
+
+[
+    float-array{
+        0.0
+        0.0
+        0.0
+        100.0
+        50.0
+        0.0
+        50.0
+        100.0
+        100.0
+        0.0
+        100.0
+        100.0
+    }
+] [
+    { 1 0 } { 100 100 } { COLOR: red COLOR: green COLOR: blue }
+    gradient-vertices
+] unit-test
diff --git a/basis/ui/pens/gradient/gradient.factor b/basis/ui/pens/gradient/gradient.factor
index 7f7bd02204..fbf190a218 100644
--- a/basis/ui/pens/gradient/gradient.factor
+++ b/basis/ui/pens/gradient/gradient.factor
@@ -16,7 +16,7 @@ TUPLE: gradient < caching-pen colors last-vertices last-colors ;
 
 :: gradient-vertices ( direction dim colors -- seq )
     direction dim v* dim over v- swap
-    colors length dup 1 - v/n [ v*n ] with map
+    colors length [ iota ] [ 1 - ] bi v/n [ v*n ] with map
     swap [ over v+ 2array ] curry map
     concat concat >float-array ;