diff --git a/CHANGELOG.md b/CHANGELOG.md
index 62bc030..ecf8ae0 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,11 @@
 # CHANGELOG
 
+## 2.1.1
+
+### Fixed
+
+- Replace usage of function `Keyword.validate/2` which is not usable with Elixir v1.9
+
 ## 2.1.0
 
 ### Changed
diff --git a/lib/exos.ex b/lib/exos.ex
index f88be95..7d7a8ff 100644
--- a/lib/exos.ex
+++ b/lib/exos.ex
@@ -38,21 +38,19 @@ defmodule Exos.Proc do
   end
 
   def start_link(cmd, init, opts \\ []) do
-    known_opts = [:port_opts, :gen_server_opts, :event_fun, :etf_opts]
-    case Keyword.keyword?(opts) and match?({:ok, _}, Keyword.validate(opts, known_opts)) do
-      true ->
-        port_opts = Keyword.get(opts, :port_opts, [])
-        gen_server_opts = Keyword.get(opts, :gen_server_opts, [])
-        event_fun = Keyword.get(opts, :event_fun)
-        etf_opts = Keyword.get(opts, :etf_opts, [])
-        GenServer.start_link(Exos.Proc, {cmd, init, port_opts, event_fun, etf_opts}, gen_server_opts)
-
-      false ->
-        # If no key matches with our opts, then it means it is the old API being used.
-        IO.warn("You are using the old API of #{__MODULE__}.start_link/3 that takes Port.open/2
-          options as 3rd parameter. The new API takes a Keyword list instead to handle options of
-          the old API.")
-        start_link(cmd, init, [port_opts: opts])
+    supported_opts = [:port_opts, :gen_server_opts, :event_fun, :etf_opts]
+    if Keyword.keyword?(opts) and Enum.all?(Keyword.keys(opts), & &1 in supported_opts) do
+      port_opts = Keyword.get(opts, :port_opts, [])
+      gen_server_opts = Keyword.get(opts, :gen_server_opts, [])
+      event_fun = Keyword.get(opts, :event_fun)
+      etf_opts = Keyword.get(opts, :etf_opts, [])
+      GenServer.start_link(Exos.Proc, {cmd, init, port_opts, event_fun, etf_opts}, gen_server_opts)
+    else
+      # If no key matches with our opts, then it means it is the old API being used.
+      IO.warn("You are using the old API of #{__MODULE__}.start_link/3 that takes Port.open/2
+        options as 3rd parameter. The new API takes a Keyword list instead to handle options of
+        the old API.")
+      start_link(cmd, init, [port_opts: opts])
     end
   end
 
diff --git a/mix.exs b/mix.exs
index e2d599a..369f5f9 100644
--- a/mix.exs
+++ b/mix.exs
@@ -1,7 +1,7 @@
 defmodule Exos.Mixfile do
   use Mix.Project
 
-  defp version, do: "2.1.0"
+  defp version, do: "2.1.1"
 
   def project do
     [