diff --git a/chrono/manager/forms.py b/chrono/manager/forms.py
index ccd8eb37..2ac53118 100644
--- a/chrono/manager/forms.py
+++ b/chrono/manager/forms.py
@@ -99,6 +99,11 @@ class TimePeriodAddForm(forms.Form):
     start_time = forms.TimeField(label=_('Start Time'), widget=widgets.TimeWidget())
     end_time = forms.TimeField(label=_('End Time'), widget=widgets.TimeWidget())
 
+    def clean_end_time(self):
+        if self.cleaned_data['end_time'] <= self.cleaned_data['start_time']:
+            raise ValidationError(_('End time must come after start time.'))
+        return self.cleaned_data['end_time']
+
 
 class TimePeriodForm(forms.ModelForm):
     class Meta:
@@ -110,6 +115,11 @@ class TimePeriodForm(forms.ModelForm):
         }
         exclude = []
 
+    def clean_end_time(self):
+        if self.cleaned_data['end_time'] <= self.cleaned_data['start_time']:
+            raise ValidationError(_('End time must come after start time.'))
+        return self.cleaned_data['end_time']
+
 
 class NewDeskForm(forms.ModelForm):
     class Meta:
diff --git a/tests/test_manager.py b/tests/test_manager.py
index 3e8ffc6f..fd43a100 100644
--- a/tests/test_manager.py
+++ b/tests/test_manager.py
@@ -676,6 +676,14 @@ def test_meetings_agenda_add_time_period(app, admin_user):
     assert u'Wednesday / 10 a.m. → 5 p.m.' in resp.text
     assert resp.text.index('Monday') < resp.text.index('Wednesday')
 
+    # invert start and end
+    resp2 = resp.click('Add a time period', index=0)
+    resp2.form['weekdays-0'].checked = True
+    resp2.form['start_time'] = '13:00'
+    resp2.form['end_time'] = '10:00'
+    resp2 = resp2.form.submit()
+    assert 'End time must come after start time.' in resp2.text
+
     # and edit
     resp = resp.click(u'Wednesday / 10 a.m. → 5 p.m.')
     assert 'Edit Time Period' in resp.text
@@ -684,6 +692,12 @@ def test_meetings_agenda_add_time_period(app, admin_user):
     resp = resp.follow()
     assert TimePeriod.objects.get(desk=desk, weekday=2).start_time.hour == 9
 
+    # and edit with inverted start/end
+    resp2 = resp.click(u'Wednesday / 9 a.m. → 5 p.m.')
+    resp2.form['start_time'] = '18:00'
+    resp2 = resp2.form.submit()
+    assert 'End time must come after start time.' in resp2.text
+
     # and add same time periods on multiple days
     resp = resp.click('Add a time period', index=0)
     resp.form['weekdays-4'].checked = True