diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index 02ae51fa0..87eda7a7f 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -622,7 +622,7 @@ jobs:
 
     - name: Install REST API and UI
       run: |
-        pip install -U rest_api/
+        pip install -U "./rest_api[dev]"
         pip install -U ui/
         pip install .   # -U prevents the schema generation
 
diff --git a/rest_api/pyproject.toml b/rest_api/pyproject.toml
index df7a38e88..6cb1a3d63 100644
--- a/rest_api/pyproject.toml
+++ b/rest_api/pyproject.toml
@@ -35,6 +35,11 @@ dependencies = [
 ]
 dynamic = ["version"]
 
+[project.optional-dependencies]
+dev = [
+  "httpx"
+]
+
 [project.urls]
 Documentation = "https://github.com/deepset-ai/haystack/tree/main/rest_api#readme"
 Issues = "https://github.com/deepset-ai/haystack/issues"