diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
new file mode 100644
index 0000000..9ca6f10
--- /dev/null
+++ b/.github/workflows/main.yml
@@ -0,0 +1,39 @@
+# Adapted form https://github.com/avsm/hello-world-action-ocaml/blob/master/.github/workflows/workflow.yml
+name: build
+
+on:
+  - pull_request
+
+jobs:
+  build:
+    strategy:
+      fail-fast: false
+      matrix:
+        os:
+          - ubuntu-latest
+          # - macos-latest
+          # - windows-latest
+        ocaml-version:
+          - 4.11.x
+          # - 4.10.1
+          # - 4.09.1
+          # - 4.08.1
+
+    runs-on: ${{ matrix.os }}
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Use OCaml ${{ matrix.ocaml-version }}
+        uses: actions-ml/setup-ocaml@master
+        with:
+          opam-disable-sandboxing: true
+          dune-cache: true
+          ocaml-version: ${{ matrix.ocaml-version }}
+
+      - run: opam install . --deps-only --with-doc --with-test
+
+      - run: opam exec -- dune build
+
+      - run: opam exec -- dune runtest
diff --git a/README.md b/README.md
index dee61bc..c6f317a 100644
--- a/README.md
+++ b/README.md
@@ -2,6 +2,8 @@
 
 _Tiny executable techniques for dealing with emoji_
 
+![build](https://github.com/shonfeder/emojitsu/workflows/build/badge.svg)
+
 <!-- markdown-toc start - Don't edit this section. Run M-x markdown-toc-refresh-toc -->
 **Table of Contents**
 
diff --git a/dune-project b/dune-project
index e2694a1..a2d0250 100644
--- a/dune-project
+++ b/dune-project
@@ -26,18 +26,20 @@ Currently supports:
   ; dev
   (curly (and :with-test (>= 0.2.0)))
   (uutf (and :with-test (>= 1.0.2)))
+  (ppx_string (and :with-test (>= v0.14.0) (< v0.15.0)))
+  (yojson (and :with-test (>= 1.7.0) (< 1.8.0)))
+  (mdx (and :with-test (>= 1.7.0) (< 1.8.0)))
 
   ; libs
   (bos (and (>= 0.2.0) (< 0.3.0)))
   (re (and (>= 1.9.0) (< 1.10.0)))
-  (yojson (and (>= 1.7.0) (< 1.8.0)))
 
   ; preprocessors
   (ppx_deriving (and (>= 5.1) (< 6.0)))
   (ppx_expect (and (>= v0.14.0) (< v0.15.0)))
   (ppx_inline_test (and (>= v0.14.0) (< v0.15.0)))
-  (ppx_string (and (>= v0.14.0) (< v0.15.0)))
 
    ; pinned, see ./emojitsu.opam.template
   kwdcmd))
+
 (using mdx 0.1)
diff --git a/emojitsu.opam b/emojitsu.opam
index 072ecb2..ac6faf0 100644
--- a/emojitsu.opam
+++ b/emojitsu.opam
@@ -19,13 +19,14 @@ depends: [
   "dune" {>= "2.7" & > "2.7"}
   "curly" {with-test & >= "0.2.0"}
   "uutf" {with-test & >= "1.0.2"}
+  "ppx_string" {with-test & >= "v0.14.0" & < "v0.15.0"}
+  "yojson" {with-test & >= "1.7.0" & < "1.8.0"}
+  "mdx" {with-test & >= "1.7.0" & < "1.8.0"}
   "bos" {>= "0.2.0" & < "0.3.0"}
   "re" {>= "1.9.0" & < "1.10.0"}
-  "yojson" {>= "1.7.0" & < "1.8.0"}
   "ppx_deriving" {>= "5.1" & < "6.0"}
   "ppx_expect" {>= "v0.14.0" & < "v0.15.0"}
   "ppx_inline_test" {>= "v0.14.0" & < "v0.15.0"}
-  "ppx_string" {>= "v0.14.0" & < "v0.15.0"}
   "kwdcmd"
   "odoc" {with-doc}
 ]