diff --git a/.github/workflows/build.yml b/.github/workflows/build.yml
index 8254241..1309106 100644
--- a/.github/workflows/build.yml
+++ b/.github/workflows/build.yml
@@ -111,12 +111,4 @@ jobs:
           opam pin -y -n melange-jest git+https://github.com/melange-community/melange-jest.git
           opam pin -y -n melange-webapi git+https://github.com/melange-community/melange-webapi.git
 
-      - run: opam install ./melange-decoders.opam --deps-only --with-test
-
-      - run: opam exec -- dune build --root .
-        working-directory: js
-
-      - run: npx jest _build
-        working-directory: js
-
-      - run: opam install ./melange-decoders.opam
+      - run: opam install ./melange-decoders.opam --with-test
diff --git a/Makefile b/Makefile
index 7cf9778..c25cbbe 100644
--- a/Makefile
+++ b/Makefile
@@ -70,8 +70,14 @@ watch-test-bs:
 clean-bs:
 	npm run clean
 
+js/melange-decoders.opam:
+	touch js/melange-decoders.opam
 
-melange-decoders.install:
-	cd js && touch melange-decoders.opam && dune build -p melange-decoders && rm melange-decoders.opam
+melange-decoders-test: js/melange-decoders.opam
+	cd js && dune build __tests__
+	npx jest js/_build
+
+melange-decoders.install: js/melange-decoders.opam
+	cd js && dune build -p melange-decoders
 	perl -i -pe s#_build#js/_build# js/melange-decoders.install
-	cp js/melange-decoders.install .
+	mv js/melange-decoders.install .
diff --git a/js/.gitignore b/js/.gitignore
new file mode 100644
index 0000000..31a737e
--- /dev/null
+++ b/js/.gitignore
@@ -0,0 +1 @@
+melange-decoders.opam
\ No newline at end of file
diff --git a/melange-decoders.opam b/melange-decoders.opam
index cdec299..0449ae9 100644
--- a/melange-decoders.opam
+++ b/melange-decoders.opam
@@ -18,5 +18,6 @@ depends: [
   "melange-jest" {with-test}
 ]
 build: [
+  [make "melange-decoders-test"] {with-test}
   [make "melange-decoders.install"]
 ]
diff --git a/melange-decoders.opam.template b/melange-decoders.opam.template
index daedf9c..f5d5de0 100644
--- a/melange-decoders.opam.template
+++ b/melange-decoders.opam.template
@@ -10,5 +10,6 @@ depends: [
   "melange-jest" {with-test}
 ]
 build: [
+  [make "melange-decoders-test"] {with-test}
   [make "melange-decoders.install"]
 ]