diff --git a/README.md b/README.md
index b8035e1..281f476 100644
--- a/README.md
+++ b/README.md
@@ -135,10 +135,8 @@ an error is raised,
 lume.reduce({1, 2, 3}, function(a, b) return a + b end) -- Returns 6
 ```
 
-### lume.set(t [, retainkeys])
-Returns a copy of the `t` table with all the duplicate values removed. If
-`retainkeys` is true the table is not treated as an array and retains its
-original keys.
+### lume.set(t)
+Returns a copy of the `t` array with all the duplicate values removed. 
 ```lua
 lume.set({2, 1, 2, "cat", "cat"}) -- Returns {1, 2, "cat"}
 ```
diff --git a/lume.lua b/lume.lua
index f9a52b4..5813492 100644
--- a/lume.lua
+++ b/lume.lua
@@ -232,10 +232,10 @@ function lume.reduce(t, fn, first)
 end
 
 
-function lume.set(t, retainkeys)
+function lume.set(t)
   local rtn = {}
   for k, v in pairs(lume.invert(t)) do
-    rtn[retainkeys and v or (#rtn + 1)] = k
+    rtn[#rtn + 1] = k
   end
   return rtn
 end