diff --git a/extra/sets/extras/extras-tests.factor b/extra/sets/extras/extras-tests.factor
index c6ce2adf25..5cc06343a6 100644
--- a/extra/sets/extras/extras-tests.factor
+++ b/extra/sets/extras/extras-tests.factor
@@ -18,3 +18,7 @@ IN: sets.extras.tests
 { f } [ { 1 2 } { 1 2 } proper-subset? ] unit-test
 { f } [ { 1 2 3 } { 1 2 } proper-subset? ] unit-test
 { t } [ { 1 2 } { 1 2 3 } proper-subset? ] unit-test
+
+{ "abc" } [ "abc" non-repeating ] unit-test
+{ "abc" } [ "abcddd" non-repeating ] unit-test
+{ "" } [ "aabbcc" non-repeating ] unit-test
diff --git a/extra/sets/extras/extras.factor b/extra/sets/extras/extras.factor
index 323db086b6..a96c5a938a 100644
--- a/extra/sets/extras/extras.factor
+++ b/extra/sets/extras/extras.factor
@@ -1,6 +1,6 @@
 ! Copyright (C) 2013 Doug Coleman.
 ! See http://factorcode.org/license.txt for BSD license.
-USING: kernel sequences sets ;
+USING: kernel locals sequences sets ;
 IN: sets.extras
 
 : setwise-xor ( seq1 seq2 -- set )
@@ -17,3 +17,11 @@ IN: sets.extras
 
 : disjoint? ( set1 set2 -- ? )
     intersects? not ;
+
+:: non-repeating ( seq -- seq' )
+    HS{ } clone :> visited
+    0 seq new-resizable :> accum
+    seq [
+        accum over visited ?adjoin
+        [ push ] [ remove! drop ] if
+    ] each accum seq like ;