diff --git a/lib/mllp/client.ex b/lib/mllp/client.ex
index 638ea73..6cf3c5f 100644
--- a/lib/mllp/client.ex
+++ b/lib/mllp/client.ex
@@ -131,7 +131,9 @@ defmodule MLLP.Client do
 
   @behaviour MLLP.ClientContract
 
-  use GenStateMachine, callback_mode: [:state_functions, :state_enter]
+  @behaviour :gen_statem
+
+
 
   @type pid_ref :: atom | pid | {atom, any} | {:via, atom, any}
   @type ip_address :: :inet.socket_address() | String.t()
@@ -253,9 +255,10 @@ defmodule MLLP.Client do
         ) :: {:ok, pid()}
 
   def start_link(address, port, options \\ []) do
-    GenStateMachine.start_link(
+    :gen_statem.start_link(
       __MODULE__,
-      [address: normalize_address!(address), port: port] ++ options
+      [address: normalize_address!(address), port: port] ++ options,
+      []
     )
   end
 
@@ -263,13 +266,13 @@ defmodule MLLP.Client do
   Returns true if the connection is open and established, otherwise false.
   """
   @spec is_connected?(pid :: pid()) :: boolean()
-  def is_connected?(pid) when is_pid(pid), do: GenStateMachine.call(pid, :is_connected)
+  def is_connected?(pid) when is_pid(pid), do: :gen_statem.call(pid, :is_connected)
 
   @doc """
   Instructs the client to disconnect (if connected) and attempt a reconnect.
   """
   @spec reconnect(pid :: pid()) :: :ok
-  def reconnect(pid), do: GenStateMachine.call(pid, :reconnect)
+  def reconnect(pid), do: :gen_statem.call(pid, :reconnect)
 
   @doc """
   Sends a message and receives a response.
@@ -304,7 +307,7 @@ defmodule MLLP.Client do
   def send(pid, %HL7.Message{} = payload, options, timeout) do
     raw_message = to_string(payload)
 
-    case GenStateMachine.call(pid, {:send, raw_message, options}, timeout) do
+    case :gen_statem.call(pid, {:send, raw_message, options}, timeout) do
       {:ok, reply} ->
         verify_ack(reply, raw_message)
 
@@ -314,7 +317,7 @@ defmodule MLLP.Client do
   end
 
   def send(pid, payload, options, timeout) do
-    case GenStateMachine.call(pid, {:send, payload, options}, timeout) do
+    case :gen_statem.call(pid, {:send, payload, options}, timeout) do
       {:ok, wrapped_message} ->
         {:ok, MLLP.Envelope.unwrap_message(wrapped_message)}
 
@@ -337,22 +340,26 @@ defmodule MLLP.Client do
   end
 
   def send_async(pid, payload, timeout) when is_binary(payload) do
-    GenStateMachine.call(pid, {:send_async, payload, []}, timeout)
+    :gen_statem.call(pid, {:send_async, payload, []}, timeout)
   end
 
   @doc """
   Stops an MLLP.Client given a MLLP.Client pid.
 
-  This function will always return `:ok` per `GenStateMachine.stop/1`, thus
+  This function will always return `:ok` per `:gen_statem.stop/1`, thus
   you may give it a pid that references a client which is already stopped.
   """
   @spec stop(pid :: pid()) :: :ok
-  def stop(pid), do: GenStateMachine.stop(pid)
+  def stop(pid), do: :gen_statem.stop(pid)
 
   @header MLLP.Envelope.sb()
   @trailer MLLP.Envelope.eb_cr()
 
-  ## GenStateMachine callbacks
+  ## :gen_statem callbacks
+  @impl true
+  def callback_mode() do
+    [:state_functions, :state_enter]
+  end
 
   @impl true
   @spec init(Keyword.t()) ::
@@ -540,7 +547,7 @@ defmodule MLLP.Client do
   end
 
   ########################################
-  ### End of GenStateMachine callbacks ###
+  ### End of :gen_statem callbacks ###
   ########################################
 
   defp unexpected_message(state, event, message) do
@@ -578,7 +585,7 @@ defmodule MLLP.Client do
   end
 
   defp reply_to_caller(reply, %{caller: caller, context: context} = state) do
-    caller && GenStateMachine.reply(caller, format_reply(reply, context))
+    caller && :gen_statem.reply(caller, format_reply(reply, context))
     reply_cleanup(state)
   end
 
diff --git a/mix.exs b/mix.exs
index ff0709c..f3b92a2 100644
--- a/mix.exs
+++ b/mix.exs
@@ -38,7 +38,6 @@ defmodule MLLP.MixProject do
       {:ranch, "~> 1.8.0"},
       {:elixir_hl7, "== 0.6.2"},
       {:backoff, "~> 1.1.6"},
-      {:gen_state_machine, "~> 3.0"},
       {:ex_doc, "~> 0.24.2", only: :dev, runtime: false},
       {:dialyxir, "~> 1.1.0", only: [:dev, :test], runtime: false},
       {:mix_test_watch, "~> 1.0.2", only: :dev, runtime: false},
diff --git a/mix.lock b/mix.lock
index 2b500b9..94050a2 100644
--- a/mix.lock
+++ b/mix.lock
@@ -8,7 +8,6 @@
   "ex_doc": {:hex, :ex_doc, "0.24.2", "e4c26603830c1a2286dae45f4412a4d1980e1e89dc779fcd0181ed1d5a05c8d9", [:mix], [{:earmark_parser, "~> 1.4.0", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_elixir, "~> 0.14", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1", [hex: :makeup_erlang, repo: "hexpm", optional: false]}], "hexpm", "e134e1d9e821b8d9e4244687fb2ace58d479b67b282de5158333b0d57c6fb7da"},
   "excoveralls": {:hex, :excoveralls, "0.14.6", "610e921e25b180a8538229ef547957f7e04bd3d3e9a55c7c5b7d24354abbba70", [:mix], [{:hackney, "~> 1.16", [hex: :hackney, repo: "hexpm", optional: false]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "0eceddaa9785cfcefbf3cd37812705f9d8ad34a758e513bb975b081dce4eb11e"},
   "file_system": {:hex, :file_system, "0.2.10", "fb082005a9cd1711c05b5248710f8826b02d7d1784e7c3451f9c1231d4fc162d", [:mix], [], "hexpm", "41195edbfb562a593726eda3b3e8b103a309b733ad25f3d642ba49696bf715dc"},
-  "gen_state_machine": {:hex, :gen_state_machine, "3.0.0", "1e57f86a494e5c6b14137ebef26a7eb342b3b0070c7135f2d6768ed3f6b6cdff", [:mix], [], "hexpm", "0a59652574bebceb7309f6b749d2a41b45fdeda8dbb4da0791e355dd19f0ed15"},
   "hackney": {:hex, :hackney, "1.18.1", "f48bf88f521f2a229fc7bae88cf4f85adc9cd9bcf23b5dc8eb6a1788c662c4f6", [:rebar3], [{:certifi, "~>2.9.0", [hex: :certifi, repo: "hexpm", optional: false]}, {:idna, "~>6.1.0", [hex: :idna, repo: "hexpm", optional: false]}, {:metrics, "~>1.0.0", [hex: :metrics, repo: "hexpm", optional: false]}, {:mimerl, "~>1.1", [hex: :mimerl, repo: "hexpm", optional: false]}, {:parse_trans, "3.3.1", [hex: :parse_trans, repo: "hexpm", optional: false]}, {:ssl_verify_fun, "~>1.1.0", [hex: :ssl_verify_fun, repo: "hexpm", optional: false]}, {:unicode_util_compat, "~>0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "a4ecdaff44297e9b5894ae499e9a070ea1888c84afdd1fd9b7b2bc384950128e"},
   "idna": {:hex, :idna, "6.1.1", "8a63070e9f7d0c62eb9d9fcb360a7de382448200fbbd1b106cc96d3d8099df8d", [:rebar3], [{:unicode_util_compat, "~>0.7.0", [hex: :unicode_util_compat, repo: "hexpm", optional: false]}], "hexpm", "92376eb7894412ed19ac475e4a86f7b413c1b9fbb5bd16dccd57934157944cea"},
   "jason": {:hex, :jason, "1.4.1", "af1504e35f629ddcdd6addb3513c3853991f694921b1b9368b0bd32beb9f1b63", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "fbb01ecdfd565b56261302f7e1fcc27c4fb8f32d56eab74db621fc154604a7a1"},