diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index acb62f926..cc5ec9c17 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -65,6 +65,10 @@ jobs:
                       **/requirements*.txt
 
             - name: Install package test dependencies
+              # Test test will actually happened in the container, here only need to install
+              # the pytest-docker dependency.
+              # To add the dependencies to the container, we need to add them to the
+              # installation command in the `test_notebooks/conftest.py`.
               run: pip install -e .[dev]
 
             - name: Set jupyter token env
@@ -133,7 +137,7 @@ jobs:
                       **/requirements*.txt
 
             - name: Install package
-              run: pip install -e .[dev,smiles]
+              run: pip install -e .[dev,smiles,optimade]
 
             - name: Run pytest
               run: pytest -v tests --cov
diff --git a/aiidalab_widgets_base/databases.py b/aiidalab_widgets_base/databases.py
index 9b7bd149a..5ca7b41e3 100644
--- a/aiidalab_widgets_base/databases.py
+++ b/aiidalab_widgets_base/databases.py
@@ -156,7 +156,22 @@ def __init__(
         title: str = None,
         **kwargs,
     ) -> None:
-        from optimade_client import default_parameters, query_filter, query_provider
+        try:
+            from optimade_client import default_parameters, query_filter, query_provider
+        except ImportError:
+            super().__init__(
+                [
+                    ipw.HTML(
+                        """
+                        <div style="margin: 10px 0; padding: 10px; background-color: #ffcc00; color: black; border-left: 6px solid #ffeb3b;">
+                            <i class="fa fa-exclamation-triangle" aria-hidden="true"></i>
+                            &nbsp;This widget requires the <code>optimade-client</code> package to be installed.
+                            Please run <code>pip install optimade-client</code> to install the missing package.
+                        </div>"""
+                    )
+                ]
+            )
+            return
 
         providers_header = ipw.HTML("<h4>Select a provider</h4>")
         providers = query_provider.OptimadeQueryProviderWidget(
diff --git a/setup.cfg b/setup.cfg
index 97de33e0f..ad6e95c5e 100644
--- a/setup.cfg
+++ b/setup.cfg
@@ -34,7 +34,6 @@ install_requires =
     more-itertools~=8.0
     pymysql~=0.9
     nglview~=3.0
-    optimade-client==2022.9.19
     spglib>=1.14,<3
     vapory~=0.1.2
 python_requires = >=3.8
@@ -56,6 +55,8 @@ dev =
     pytest-timeout~=2.2
     selenium~=4.7.0
     webdriver-manager~=3.8
+optimade =
+    optimade-client==2022.9.19
 smiles =
     rdkit>=2021.09.2
     scikit-learn~=1.0.0
diff --git a/tests_notebooks/conftest.py b/tests_notebooks/conftest.py
index 5d94186bc..3992340d0 100644
--- a/tests_notebooks/conftest.py
+++ b/tests_notebooks/conftest.py
@@ -61,7 +61,7 @@ def notebook_service(docker_ip, docker_services, aiidalab_exec):
     aiidalab_exec("chmod -R a+rw /home/jovyan/apps/aiidalab-widgets-base", user="root")
 
     # Install AWB with extra dependencies for SmilesWidget
-    aiidalab_exec("pip install --no-cache-dir .[smiles]")
+    aiidalab_exec("pip install --no-cache-dir .[smiles,optimade]")
 
     # `port_for` takes a container port and returns the corresponding host port
     port = docker_services.port_for("aiidalab", 8888)