diff --git a/tests/admin_pages/test_form.py b/tests/admin_pages/test_form.py
index e878a7b37..50d6e99f0 100644
--- a/tests/admin_pages/test_form.py
+++ b/tests/admin_pages/test_form.py
@@ -2321,6 +2321,40 @@ def test_form_edit_items_field(pub):
     assert FormDef.get(1).fields[0].items == ['XXX']
 
 
+def test_form_edit_items_datasource(pub):
+    create_superuser(pub)
+    create_role(pub)
+
+    FormDef.wipe()
+    formdef = FormDef()
+    formdef.name = 'form title'
+    formdef.fields = [fields.ItemsField(id='1', label='1st field', type='items')]
+    formdef.store()
+
+    app = login(get_app(pub))
+    resp = app.get('/backoffice/forms/1/')
+    resp = resp.click(href='fields/')
+    assert '1st field' in resp.text
+
+    resp = app.get('/backoffice/forms/1/fields/1/')
+    resp.form['data_mode'].value = 'data-source'
+    resp.form['data_source$type'].value = 'json'
+    resp.form['data_source$value'].value = 'random string'
+    resp = resp.form.submit('submit')
+    assert 'Value must be a full URL.' in resp.text
+    resp.form['data_source$value'].value = 'http://whatever'
+    resp = resp.form.submit('submit').follow()
+    assert FormDef.get(1).fields[0].data_source == {'type': 'json', 'value': 'http://whatever'}
+
+    # check template strings are ok
+    resp = app.get('/backoffice/forms/1/fields/1/')
+    resp.form['data_mode'].value = 'data-source'
+    resp.form['data_source$type'].value = 'json'
+    resp.form['data_source$value'].value = '{{url}}'
+    resp = resp.form.submit('submit').follow()
+    assert FormDef.get(1).fields[0].data_source == {'type': 'json', 'value': '{{url}}'}
+
+
 def test_form_edit_page_field(pub):
     create_superuser(pub)
     create_role(pub)
diff --git a/wcs/data_sources.py b/wcs/data_sources.py
index 259940396..8fec665a6 100644
--- a/wcs/data_sources.py
+++ b/wcs/data_sources.py
@@ -179,6 +179,14 @@ class DataSourceSelectionWidget(CompositeWidget):
             value = self.get(name)
             if value:
                 values[name] = value
+
+        if values.get('type') in ('json', 'jsonp', 'geojson'):
+            url = values.get('value') or ''
+            if url and not Template.is_template_string(url):
+                parsed = urllib.parse.urlparse(url)
+                if not (parsed.scheme and parsed.netloc):
+                    self.error = _('Value must be a full URL.')
+
         if values.get('type', '') in ('none', ''):
             values = None
         self.value = values or None