diff --git a/Makefile b/Makefile
index 6fbacd16..f61ce57b 100644
--- a/Makefile
+++ b/Makefile
@@ -16,4 +16,4 @@ gen-protos: protoc-gen-elixir
 	protoc -I src -I test/protobuf/protoc/proto --elixir_out=test/protobuf/protoc/proto_gen --plugin=./protoc-gen-elixir test/protobuf/protoc/proto/*.proto
 	protoc -I src --elixir_out=lib --plugin=./protoc-gen-elixir elixirpb.proto
 
-.PHONY: clean gen_google_proto gen_test_protos
+.PHONY: clean protoc-gen-elixir gen-google-protos gen-protos
diff --git a/lib/mix/tasks/protobuf.ex b/lib/mix/tasks/protobuf.ex
new file mode 100644
index 00000000..189e202e
--- /dev/null
+++ b/lib/mix/tasks/protobuf.ex
@@ -0,0 +1,7 @@
+defmodule Mix.Tasks.Protobuf do
+  use Mix.Task
+
+  def run(args) do
+    Protobuf.Protoc.CLI.main(args)
+  end
+end
diff --git a/lib/protobuf/dsl.ex b/lib/protobuf/dsl.ex
index caf33cd2..0f656bd4 100644
--- a/lib/protobuf/dsl.ex
+++ b/lib/protobuf/dsl.ex
@@ -258,6 +258,10 @@ defmodule Protobuf.DSL do
     |> cal_encoded_fnum()
   end
 
+  defp parse_field_opts([{:extensions, map} | t], acc) do
+    parse_field_opts(t, Map.put(acc, :extensions, map))
+  end
+
   defp parse_field_opts([{:optional, true} | t], acc) do
     parse_field_opts(t, Map.put(acc, :optional?, true))
   end
diff --git a/lib/protobuf/field_props.ex b/lib/protobuf/field_props.ex
index 693bed75..b0a05a2e 100644
--- a/lib/protobuf/field_props.ex
+++ b/lib/protobuf/field_props.ex
@@ -17,7 +17,8 @@ defmodule Protobuf.FieldProps do
           packed?: boolean,
           map?: boolean,
           deprecated?: boolean,
-          encoded_fnum: iodata
+          encoded_fnum: iodata,
+          extensions: map
         }
   defstruct fnum: nil,
             name: nil,
@@ -34,5 +35,6 @@ defmodule Protobuf.FieldProps do
             packed?: nil,
             map?: false,
             deprecated?: false,
-            encoded_fnum: nil
+            encoded_fnum: nil,
+            extensions: %{}
 end
diff --git a/lib/protobuf/protoc/cli.ex b/lib/protobuf/protoc/cli.ex
index 58a15047..4f7e7473 100644
--- a/lib/protobuf/protoc/cli.ex
+++ b/lib/protobuf/protoc/cli.ex
@@ -18,6 +18,7 @@ defmodule Protobuf.Protoc.CLI do
 
   @doc false
   def main(["--version"]) do
+    Application.ensure_all_started(:protobuf)
     {:ok, version} = :application.get_key(:protobuf, :vsn)
     IO.puts(to_string(version))
   end
@@ -27,6 +28,9 @@ defmodule Protobuf.Protoc.CLI do
   end
 
   def main(_) do
+    Application.ensure_all_started(:protobuf)
+    load_custom_extensions()
+
     # https://groups.google.com/forum/#!topic/elixir-lang-talk/T5enez_BBTI
     :io.setopts(:standard_io, encoding: :latin1)
     bin = IO.binread(:all)
@@ -134,4 +138,14 @@ defmodule Protobuf.Protoc.CLI do
     |> Enum.filter(&(&1 && &1 != ""))
     |> Enum.join(".")
   end
+
+  defp load_custom_extensions do
+    Application.get_env(:protobuf, :extension_paths, [])
+    |> Enum.map(&Path.wildcard/1)
+    |> List.flatten()
+    |> Enum.map(&Code.require_file/1)
+    |> List.flatten()
+    |> Enum.map(fn {module, _} -> module end)
+    |> Protobuf.Extension.cal_extensions()
+  end
 end
diff --git a/lib/protobuf/protoc/generator/message.ex b/lib/protobuf/protoc/generator/message.ex
index 33d631a5..9bc94ebf 100644
--- a/lib/protobuf/protoc/generator/message.ex
+++ b/lib/protobuf/protoc/generator/message.ex
@@ -288,6 +288,13 @@ defmodule Protobuf.Protoc.Generator.Message do
   end
 
   defp merge_field_options(opts, f) do
+    opts =
+      if map_size(f.options.__pb_extensions__) > 0 do
+        Map.put(opts, :extensions, inspect(f.options.__pb_extensions__))
+      else
+        opts
+      end
+
     opts
     |> Map.put(:packed, f.options.packed)
     |> Map.put(:deprecated, f.options.deprecated)
diff --git a/test/protobuf/protoc/generator/message_test.exs b/test/protobuf/protoc/generator/message_test.exs
index 605b1780..52b80330 100644
--- a/test/protobuf/protoc/generator/message_test.exs
+++ b/test/protobuf/protoc/generator/message_test.exs
@@ -143,13 +143,20 @@ defmodule Protobuf.Protoc.Generator.MessageTest do
             number: 1,
             type: :TYPE_INT32,
             label: :LABEL_OPTIONAL,
-            options: Google.Protobuf.FieldOptions.new(packed: true)
+            options:
+              Google.Protobuf.FieldOptions.new(
+                packed: true,
+                __pb_extensions__: %{{Mypkg.PbExtension, :myopt_bool} => true}
+              )
           )
         ]
       )
 
     {[], [msg]} = Generator.generate(ctx, desc)
-    assert msg =~ "field :a, 1, optional: true, type: :int32, packed: true\n"
+
+    assert msg =~
+             "field :a, 1, optional: true, type: :int32, " <>
+               "extensions: %{{Mypkg.PbExtension, :myopt_bool} => true}, packed: true\n"
   end
 
   test "generate/2 supports option :deprecated" do
diff --git a/test/protobuf/protoc/integration_test.exs b/test/protobuf/protoc/integration_test.exs
index f4f70498..00c51dee 100644
--- a/test/protobuf/protoc/integration_test.exs
+++ b/test/protobuf/protoc/integration_test.exs
@@ -50,6 +50,10 @@ defmodule Protobuf.Protoc.IntegrationTest do
 
   test "options" do
     assert %{deprecated?: true} = My.Test.Options.__message_props__().field_props[1]
+
+    assert %{
+             extensions: %{{Mypkg.PbExtension, :myopt_bool} => true}
+           } = My.Test.Options.__message_props__().field_props[2]
   end
 
   test "extensions" do
diff --git a/test/protobuf/protoc/proto/extension.proto b/test/protobuf/protoc/proto/extension.proto
index 6d3be1f4..e6b239ca 100644
--- a/test/protobuf/protoc/proto/extension.proto
+++ b/test/protobuf/protoc/proto/extension.proto
@@ -4,9 +4,12 @@ package ext;
 
 // -I src is needed, see Makefile
 import "elixirpb.proto";
+import "mypkg.proto";
 
 option (elixirpb.file).module_prefix = "Protobuf.Protoc.ExtTest";
 
 message Foo {
   optional string a = 1;
+  optional string b = 2 [(mypkg.myopt_bool)=true];
+  optional string c = 3 [(mypkg.myopt_string)="test"];
 }
diff --git a/test/protobuf/protoc/proto/mypkg.proto b/test/protobuf/protoc/proto/mypkg.proto
new file mode 100644
index 00000000..3a1d6434
--- /dev/null
+++ b/test/protobuf/protoc/proto/mypkg.proto
@@ -0,0 +1,10 @@
+syntax = "proto2";
+
+package mypkg;
+
+import "google/protobuf/descriptor.proto";
+
+extend google.protobuf.FieldOptions {
+  optional bool myopt_bool = 100000;
+  optional string myopt_string = 100001 [default="test"];
+}
diff --git a/test/protobuf/protoc/proto/test.proto b/test/protobuf/protoc/proto/test.proto
index 227ad428..d0773372 100644
--- a/test/protobuf/protoc/proto/test.proto
+++ b/test/protobuf/protoc/proto/test.proto
@@ -6,6 +6,9 @@ package my.test;  // dotted package name
 //import "imp.proto";
 import "multi/multi1.proto";  // unused import
 
+// extensions
+import "mypkg.proto";
+
 enum HatType {
   // deliberately skipping 0
   FEDORA = 1;
@@ -125,4 +128,5 @@ message Communique {
 
 message Options {
   optional string opt1 = 1 [deprecated=true];
+  optional string opt2 = 2 [(mypkg.myopt_bool)=true];
 }
diff --git a/test/protobuf/protoc/proto_gen/extension.pb.ex b/test/protobuf/protoc/proto_gen/extension.pb.ex
index 8fbddfe9..4f5a989d 100644
--- a/test/protobuf/protoc/proto_gen/extension.pb.ex
+++ b/test/protobuf/protoc/proto_gen/extension.pb.ex
@@ -3,9 +3,21 @@ defmodule Protobuf.Protoc.ExtTest.Foo do
   use Protobuf, syntax: :proto2
 
   @type t :: %__MODULE__{
-          a: String.t()
+          a: String.t(),
+          b: String.t(),
+          c: String.t()
         }
-  defstruct [:a]
+  defstruct [:a, :b, :c]
 
   field :a, 1, optional: true, type: :string
+
+  field :b, 2,
+    optional: true,
+    type: :string,
+    extensions: %{{Mypkg.PbExtension, :myopt_bool} => true}
+
+  field :c, 3,
+    optional: true,
+    type: :string,
+    extensions: %{{Mypkg.PbExtension, :myopt_string} => "test"}
 end
diff --git a/test/protobuf/protoc/proto_gen/mypkg.pb.ex b/test/protobuf/protoc/proto_gen/mypkg.pb.ex
new file mode 100644
index 00000000..1bbab361
--- /dev/null
+++ b/test/protobuf/protoc/proto_gen/mypkg.pb.ex
@@ -0,0 +1,11 @@
+defmodule Mypkg.PbExtension do
+  @moduledoc false
+  use Protobuf, syntax: :proto2
+
+  extend Google.Protobuf.FieldOptions, :myopt_bool, 100_000, optional: true, type: :bool
+
+  extend Google.Protobuf.FieldOptions, :myopt_string, 100_001,
+    optional: true,
+    type: :string,
+    default: "test"
+end
diff --git a/test/protobuf/protoc/proto_gen/test.pb.ex b/test/protobuf/protoc/proto_gen/test.pb.ex
index ecb9a8e6..246ffe95 100644
--- a/test/protobuf/protoc/proto_gen/test.pb.ex
+++ b/test/protobuf/protoc/proto_gen/test.pb.ex
@@ -246,11 +246,17 @@ defmodule My.Test.Options do
   use Protobuf, syntax: :proto2
 
   @type t :: %__MODULE__{
-          opt1: String.t()
+          opt1: String.t(),
+          opt2: String.t()
         }
-  defstruct [:opt1]
+  defstruct [:opt1, :opt2]
 
   field :opt1, 1, optional: true, type: :string, deprecated: true
+
+  field :opt2, 2,
+    optional: true,
+    type: :string,
+    extensions: %{{Mypkg.PbExtension, :myopt_bool} => true}
 end
 
 defmodule My.Test.PbExtension do