diff --git a/v2/util/sequence.jam b/v2/util/sequence.jam
index 3e2ca72b5..4b2d4e935 100644
--- a/v2/util/sequence.jam
+++ b/v2/util/sequence.jam
@@ -149,17 +149,30 @@ rule length ( s * )
     return $(result) ;
 }
 
-rule unique ( list * )
+rule unique ( list * : stable ? )
 {
     local result ;
     local prev ;
-    for local i in [ SORT $(list) ]
+    if $(stable)
     {
-        if $(i) != $(prev)
+        for local f in $(list)
         {
-            result += $(i) ;
+            if ! $(f) in $(result)
+            {
+                result += $(f) ;
+            }
+        }
+    }
+    else
+    {
+        for local i in [ SORT $(list) ]
+        {
+            if $(i) != $(prev)
+            {
+                result += $(i) ;
+            }
+            prev = $(i) ;
         }
-        prev = $(i) ;
     }
     return $(result) ;
 }