diff --git a/README.md b/README.md
index 20ba6fcb..a3e53734 100644
--- a/README.md
+++ b/README.md
@@ -211,37 +211,43 @@ Below is an example on how to set and get extension fields
 
 
 ```protobuf
-// File ext.proto
+// file: ext.proto
 syntax = "proto2";
 message Foo {
+  required uint32 i = 1;
   extensions 100 to 200;
+
 }
 extend Foo {
-  option uint32 bar = 128;
-  option string baz = 128;
+  optional uint32 bar = 128;
+  optional string baz = 129;
 }
 ```
 
 ```ocaml
-(* test.ml *)
+(* file: test.ml *)
+
+open Extensions
 
 (* Set extensions *)
-let foo = Foo.{ extensions' = Ocaml_protoc_plugin.Extensions.default }
-let foo_with_bar = Bar.set foo (Some 42) in
-let foo_with_baz = Bar.set foo (Some "Test String") in
-let foo_with_bar_baz = Bar.set foo_with_bar (Some "Test String") in
-
-(* Get extensions *)
-let open Ocaml_protoc_plugin.Result in
-Bar.get foo_with_bar >>= fun bar ->
-Bar.get foo_with_baz >>= fun baz ->
-assert (bar = Some 42);
-assert (baz = Some "Test String");
-Bar.get foo_with_bar_baz >>= fun bar' ->
-Bar.get foo_with_bar_baz >>= fun baz' ->
-assert (bar' = Some 42);
-assert (baz' = Some "Test String");
-()
+let _ =
+  let foo = Foo.{ i = 31; extensions' = Ocaml_protoc_plugin.Extensions.default } in
+  let foo_with_bar = Bar.set foo (Some 42) in
+  let foo_with_baz = Baz.set foo (Some "Test String") in
+  let foo_with_bar_baz = Baz.set foo_with_bar (Some "Test String") in
+
+  (* Get extensions *)
+  let open Ocaml_protoc_plugin.Result in
+  Bar.get foo_with_bar >>= fun bar ->
+  Baz.get foo_with_baz >>= fun baz ->
+  assert (bar = Some 42);
+  assert (baz = Some "Test String");
+  Bar.get foo_with_bar_baz >>= fun bar' ->
+  Baz.get foo_with_bar_baz >>= fun baz' ->
+  assert (bar' = Some 42);
+  assert (baz' = Some "Test String");
+  return ()
+
 ```
 Extensions are replaced by proto3 `Any` type, and use is discouraged.
 
diff --git a/examples/extensions/dune b/examples/extensions/dune
new file mode 100644
index 00000000..095dd363
--- /dev/null
+++ b/examples/extensions/dune
@@ -0,0 +1,16 @@
+(executable
+ (name        test)
+ (libraries   ocaml-protoc-plugin ocaml-protoc-plugin.google_types unix)
+)
+
+(rule
+ (targets extensions.ml)
+ (deps
+  (:proto extensions.proto))
+ (action
+  (run protoc -I . "--ocaml_out=:." %{proto})))
+
+(alias
+ (name runtest)
+ (deps test.exe)
+)
diff --git a/examples/extensions/extensions.proto b/examples/extensions/extensions.proto
new file mode 100644
index 00000000..15593601
--- /dev/null
+++ b/examples/extensions/extensions.proto
@@ -0,0 +1,10 @@
+syntax = "proto2";
+message Foo {
+  required uint32 i = 1;
+  extensions 100 to 200;
+
+}
+extend Foo {
+  optional uint32 bar = 128;
+  optional string baz = 129;
+}
diff --git a/examples/extensions/test.ml b/examples/extensions/test.ml
new file mode 100644
index 00000000..cfa7d832
--- /dev/null
+++ b/examples/extensions/test.ml
@@ -0,0 +1,20 @@
+open Extensions
+
+(* Set extensions *)
+let _ =
+  let foo = Foo.{ i = 31; extensions' = Ocaml_protoc_plugin.Extensions.default } in
+  let foo_with_bar = Bar.set foo (Some 42) in
+  let foo_with_baz = Baz.set foo (Some "Test String") in
+  let foo_with_bar_baz = Baz.set foo_with_bar (Some "Test String") in
+
+  (* Get extensions *)
+  let open Ocaml_protoc_plugin.Result in
+  Bar.get foo_with_bar >>= fun bar ->
+  Baz.get foo_with_baz >>= fun baz ->
+  assert (bar = Some 42);
+  assert (baz = Some "Test String");
+  Bar.get foo_with_bar_baz >>= fun bar' ->
+  Baz.get foo_with_bar_baz >>= fun baz' ->
+  assert (bar' = Some 42);
+  assert (baz' = Some "Test String");
+  return ()