diff --git a/config/config.exs b/config/config.exs
new file mode 100644
index 0000000..aa31f17
--- /dev/null
+++ b/config/config.exs
@@ -0,0 +1,12 @@
+use Mix.Config
+
+config :msgpax, exclude_packers: []
+
+case System.get_env("TEST_EXCLUDE", "") do
+  "" ->
+    nil
+  other ->
+    config :msgpax, exclude_packers: String.split(other, ",") |> Enum.map(& &1 |> String.to_atom() )
+end
+
+#  import_config "#{Mix.env()}.exs"
diff --git a/lib/msgpax.ex b/lib/msgpax.ex
index d1f9b33..290a5b0 100644
--- a/lib/msgpax.ex
+++ b/lib/msgpax.ex
@@ -26,6 +26,15 @@ defmodule Msgpax do
   `#Msgpax.Ext<4, "02:12">`         | extension     | `#Msgpax.Ext<4, "02:12">`
   `#DateTime<2017-12-06 00:00:00Z>` | extension     | `#DateTime<2017-12-06 00:00:00Z>`
 
+  ## Excluding Default Packers
+
+  Default packers can be excluded by passing a config option:
+    `config: :msgpack, exclude_packers: [:atom, :float]`
+
+  The packers that can be exlucded are: :atom, :bitstring, :map, :list, :float, :integer, and :bin
+
+  This can be used to override default behaviors, like serializing to float32s. Use this sparingly as it's global and can break things.
+
   """
 
   alias __MODULE__.Packer
diff --git a/lib/msgpax/packer.ex b/lib/msgpax/packer.ex
index 6c11456..7ff4aea 100644
--- a/lib/msgpax/packer.ex
+++ b/lib/msgpax/packer.ex
@@ -105,131 +105,149 @@ defprotocol Msgpax.Packer do
   def pack(term)
 end
 
-defimpl Msgpax.Packer, for: Atom do
-  def pack(nil), do: [0xC0]
-  def pack(false), do: [0xC2]
-  def pack(true), do: [0xC3]
-
-  def pack(atom) do
-    atom
-    |> Atom.to_string()
-    |> @protocol.BitString.pack()
+require MsgPax.PackerMacros
+
+MsgPax.PackerMacros.excluded?(:atom) do
+  defimpl Msgpax.Packer, for: Atom do
+    def pack(nil), do: [0xC0]
+    def pack(false), do: [0xC2]
+    def pack(true), do: [0xC3]
+
+    def pack(atom) do
+      atom
+      |> Atom.to_string()
+      |> @protocol.BitString.pack()
+    end
   end
 end
 
-defimpl Msgpax.Packer, for: BitString do
-  def pack(binary) when is_binary(binary) do
-    [format(binary) | binary]
-  end
+MsgPax.PackerMacros.excluded?(:bitstring) do
+  defimpl Msgpax.Packer, for: BitString do
+    def pack(binary) when is_binary(binary) do
+      [format(binary) | binary]
+    end
 
-  def pack(bits) do
-    throw({:not_encodable, bits})
-  end
+    def pack(bits) do
+      throw({:not_encodable, bits})
+    end
 
-  defp format(binary) do
-    size = byte_size(binary)
+    defp format(binary) do
+      size = byte_size(binary)
 
-    cond do
-      size < 32 -> 0b10100000 + size
-      size < 256 -> [0xD9, size]
-      size < 0x10000 -> <<0xDA, size::16>>
-      size < 0x100000000 -> <<0xDB, size::32>>
-      true -> throw({:too_big, binary})
+      cond do
+        size < 32 -> 0b10100000 + size
+        size < 256 -> [0xD9, size]
+        size < 0x10000 -> <<0xDA, size::16>>
+        size < 0x100000000 -> <<0xDB, size::32>>
+        true -> throw({:too_big, binary})
+      end
     end
   end
 end
 
-defimpl Msgpax.Packer, for: Map do
-  defmacro __deriving__(module, struct, options) do
-    @protocol.Any.deriving(module, struct, options)
-  end
+MsgPax.PackerMacros.excluded?(:map) do
+  defimpl Msgpax.Packer, for: Map do
+    defmacro __deriving__(module, struct, options) do
+      @protocol.Any.deriving(module, struct, options)
+    end
 
-  def pack(map) do
-    [format(map) | map |> Map.to_list() |> pack([])]
-  end
+    def pack(map) do
+      [format(map) | map |> Map.to_list() |> pack([])]
+    end
 
-  defp pack([{key, value} | rest], result) do
-    pack(rest, [@protocol.pack(key), @protocol.pack(value) | result])
-  end
+    defp pack([{key, value} | rest], result) do
+      pack(rest, [@protocol.pack(key), @protocol.pack(value) | result])
+    end
 
-  defp pack([], result), do: result
+    defp pack([], result), do: result
 
-  defp format(map) do
-    length = map_size(map)
+    defp format(map) do
+      length = map_size(map)
 
-    cond do
-      length < 16 -> 0b10000000 + length
-      length < 0x10000 -> <<0xDE, length::16>>
-      length < 0x100000000 -> <<0xDF, length::32>>
-      true -> throw({:too_big, map})
+      cond do
+        length < 16 -> 0b10000000 + length
+        length < 0x10000 -> <<0xDE, length::16>>
+        length < 0x100000000 -> <<0xDF, length::32>>
+        true -> throw({:too_big, map})
+      end
     end
   end
 end
 
-defimpl Msgpax.Packer, for: List do
-  def pack(list) do
-    [format(list) | list |> Enum.reverse() |> pack([])]
-  end
+MsgPax.PackerMacros.excluded?(:list) do
+  defimpl Msgpax.Packer, for: List do
+    def pack(list) do
+      [format(list) | list |> Enum.reverse() |> pack([])]
+    end
 
-  defp pack([item | rest], result) do
-    pack(rest, [@protocol.pack(item) | result])
-  end
+    defp pack([item | rest], result) do
+      pack(rest, [@protocol.pack(item) | result])
+    end
 
-  defp pack([], result), do: result
+    defp pack([], result), do: result
 
-  defp format(list) do
-    length = length(list)
+    defp format(list) do
+      length = length(list)
 
-    cond do
-      length < 16 -> 0b10010000 + length
-      length < 0x10000 -> <<0xDC, length::16>>
-      length < 0x100000000 -> <<0xDD, length::32>>
-      true -> throw({:too_big, list})
+      cond do
+        length < 16 -> 0b10010000 + length
+        length < 0x10000 -> <<0xDC, length::16>>
+        length < 0x100000000 -> <<0xDD, length::32>>
+        true -> throw({:too_big, list})
+      end
     end
   end
 end
 
-defimpl Msgpax.Packer, for: Float do
-  def pack(num) do
-    <<0xCB, num::64-float>>
+MsgPax.PackerMacros.excluded?(:float) do
+  defimpl Msgpax.Packer, for: Float do
+
+    def pack(num) do
+      <<0xCB, num::64-float>>
+    end
   end
 end
 
-defimpl Msgpax.Packer, for: Integer do
-  def pack(int) when int < 0 do
-    cond do
-      int >= -32 -> [0x100 + int]
-      int >= -128 -> [0xD0, 0x100 + int]
-      int >= -0x8000 -> <<0xD1, int::16>>
-      int >= -0x80000000 -> <<0xD2, int::32>>
-      int >= -0x8000000000000000 -> <<0xD3, int::64>>
-      true -> throw({:too_big, int})
+MsgPax.PackerMacros.excluded?(:integer) do
+  defimpl Msgpax.Packer, for: Integer do
+    @spec pack(any) :: <<_::24, _::_*16>> | [...]
+    def pack(int) when int < 0 do
+      cond do
+        int >= -32 -> [0x100 + int]
+        int >= -128 -> [0xD0, 0x100 + int]
+        int >= -0x8000 -> <<0xD1, int::16>>
+        int >= -0x80000000 -> <<0xD2, int::32>>
+        int >= -0x8000000000000000 -> <<0xD3, int::64>>
+        true -> throw({:too_big, int})
+      end
     end
-  end
 
-  def pack(int) do
-    cond do
-      int < 128 -> [int]
-      int < 256 -> [0xCC, int]
-      int < 0x10000 -> <<0xCD, int::16>>
-      int < 0x100000000 -> <<0xCE, int::32>>
-      int < 0x10000000000000000 -> <<0xCF, int::64>>
-      true -> throw({:too_big, int})
+    def pack(int) do
+      cond do
+        int < 128 -> [int]
+        int < 256 -> [0xCC, int]
+        int < 0x10000 -> <<0xCD, int::16>>
+        int < 0x100000000 -> <<0xCE, int::32>>
+        int < 0x10000000000000000 -> <<0xCF, int::64>>
+        true -> throw({:too_big, int})
+      end
     end
   end
 end
 
-defimpl Msgpax.Packer, for: Msgpax.Bin do
-  def pack(%{data: data}) when is_binary(data), do: [format(data) | data]
+MsgPax.PackerMacros.excluded?(:bin) do
+  defimpl Msgpax.Packer, for: Msgpax.Bin do
+    def pack(%{data: data}) when is_binary(data), do: [format(data) | data]
 
-  defp format(binary) do
-    size = byte_size(binary)
+    defp format(binary) do
+      size = byte_size(binary)
 
-    cond do
-      size < 256 -> [0xC4, size]
-      size < 0x10000 -> <<0xC5, size::16>>
-      size < 0x100000000 -> <<0xC6, size::32>>
-      true -> throw({:too_big, binary})
+      cond do
+        size < 256 -> [0xC4, size]
+        size < 0x10000 -> <<0xC5, size::16>>
+        size < 0x100000000 -> <<0xC6, size::32>>
+        true -> throw({:too_big, binary})
+      end
     end
   end
 end
diff --git a/lib/msgpax/packer_macros.ex b/lib/msgpax/packer_macros.ex
new file mode 100644
index 0000000..6e3b146
--- /dev/null
+++ b/lib/msgpax/packer_macros.ex
@@ -0,0 +1,8 @@
+
+defmodule MsgPax.PackerMacros do
+  defmacro excluded?(packer_type, do: block) do
+    unless packer_type in Application.get_env(:msgpax, :exclude_packers, []) do
+      block # AST as by quote do: unquote(block)
+    end
+  end
+end
diff --git a/lib/msgpax/plug_parser.ex b/lib/msgpax/plug_parser.ex
index 62ee0e3..3adb68b 100644
--- a/lib/msgpax/plug_parser.ex
+++ b/lib/msgpax/plug_parser.ex
@@ -1,4 +1,4 @@
-if Code.ensure_compiled?(Plug) do
+if Code.ensure_compiled(Plug) == {:module, Plug} do
   defmodule Msgpax.PlugParser do
     @moduledoc """
     A `Plug.Parsers` plug for parsing a MessagePack-encoded body.
@@ -81,7 +81,7 @@ if Code.ensure_compiled?(Plug) do
          when is_atom(module) and is_atom(function) and is_list(extra_args) do
       arity = length(extra_args) + 1
 
-      unless Code.ensure_compiled?(module) and function_exported?(module, function, arity) do
+      unless Code.ensure_compiled(module) == {:module, module} and function_exported?(module, function, arity) do
         raise ArgumentError,
               "invalid :unpacker option. Undefined function " <>
                 Exception.format_mfa(module, function, arity)
@@ -89,7 +89,7 @@ if Code.ensure_compiled?(Plug) do
     end
 
     defp validate_unpacker!(unpacker) when is_atom(unpacker) do
-      unless Code.ensure_compiled?(unpacker) do
+      unless Code.ensure_compiled(unpacker) == {:module, unpacker} do
         raise ArgumentError,
               "invalid :unpacker option. The module #{inspect(unpacker)} is not " <>
                 "loaded and could not be found"