diff --git a/bijoe/schemas.py b/bijoe/schemas.py
index 2759254..109e3ba 100644
--- a/bijoe/schemas.py
+++ b/bijoe/schemas.py
@@ -288,8 +288,11 @@ class Dimension(Base):
     def build_filter(self, filter_values):
         value = self.filter_value or self.value
 
-        if self.type == 'date':
-            assert isinstance(filter_values, dict) and set(filter_values.keys()) == {'start', 'end'}
+        if (
+            self.type == 'date'
+            and isinstance(filter_values, dict)
+            and set(filter_values.keys()) == {'start', 'end'}
+        ):
             filters = []
             values = []
 
@@ -326,6 +329,8 @@ class Dimension(Base):
                         filter_value = int(filter_value)
                     elif self.type == 'bool':
                         filter_value = bool(filter_value)
+                    elif self.type == 'date':
+                        filter_value = filter_value.isoformat()
                     else:
                         raise NotImplementedError
                 except (ValueError, TypeError):
diff --git a/tests/test_schema1.py b/tests/test_schema1.py
index 0596056..4908293 100644
--- a/tests/test_schema1.py
+++ b/tests/test_schema1.py
@@ -498,3 +498,18 @@ def test_date_dimension(schema1, app, admin):
         ['09/01/2017', '1'],
         ['10/01/2017', '1'],
     ]
+
+
+def test_date_dimension_loop(schema1, app, admin):
+    login(app, admin)
+    response = app.get('/')
+    response = response.click('schema1')
+    response = response.click('Facts 1')
+    form = response.form
+    form.set('representation', 'table')
+    form.set('measure', 'simple_count')
+    form.set('loop', 'date')
+    form.set('filter__date_0', '2017-01-01')
+    form.set('filter__date_1', '2017-02-01')
+    response = form.submit('visualize')
+    assert get_table(response) == [['number of rows', '1']] * 10