diff --git a/invenio_app_rdm/records_ui/views/filters.py b/invenio_app_rdm/records_ui/views/filters.py
index ad366cd0e..1967804d5 100644
--- a/invenio_app_rdm/records_ui/views/filters.py
+++ b/invenio_app_rdm/records_ui/views/filters.py
@@ -160,12 +160,12 @@ def namespace_url(field):
     """Get custom field namespace url."""
     namespace_array = field.split(":")
     namespace = namespace_array[0]
-    namespace_value = namespace_array[1]
     namespaces = current_app.config.get("RDM_NAMESPACES")
 
     if not namespaces.get(namespace):
         return None
 
+    namespace_value = namespace_array[1]
     return namespaces[namespace] + namespace_value
 
 
diff --git a/tests/ui/conftest.py b/tests/ui/conftest.py
index 2c7debb55..82ef7e593 100644
--- a/tests/ui/conftest.py
+++ b/tests/ui/conftest.py
@@ -50,6 +50,10 @@ def load(self, filepath):
 def app_config(app_config):
     """Create test app."""
     app_config["WEBPACKEXT_MANIFEST_LOADER"] = MockManifestLoader
+    app_config["RDM_NAMESPACES"] = {
+        "test": "https://example.com/terms/#",
+        "empty": None,
+    }
     return app_config
 
 
diff --git a/tests/ui/test_filters.py b/tests/ui/test_filters.py
index 818f727ee..4ec1115e6 100644
--- a/tests/ui/test_filters.py
+++ b/tests/ui/test_filters.py
@@ -1,4 +1,4 @@
-from invenio_app_rdm.records_ui.views.filters import get_scheme_label
+from invenio_app_rdm.records_ui.views.filters import get_scheme_label, namespace_url
 
 
 def test_get_scheme_label(app):
@@ -8,3 +8,10 @@ def test_get_scheme_label(app):
     assert "arXiv" == get_scheme_label("arxiv")
 
     assert "Bibcode" == get_scheme_label("ads")
+
+
+def test_namespace_url(app):
+    """Test namespace URL filters."""
+    assert namespace_url("no_namespaced_field") is None
+    assert namespace_url("empty:field_name") is None
+    assert namespace_url("test:field_name") == "https://example.com/terms/#field_name"