diff --git a/core/models.py b/core/models.py
index 065f4eae..fb4aa809 100644
--- a/core/models.py
+++ b/core/models.py
@@ -1,9 +1,28 @@
 # -*- coding: utf-8 -*-
 from __future__ import unicode_literals
 
+from datetime import timedelta
+
+from django.core.exceptions import ValidationError
 from django.db import models
 from django.template.defaultfilters import slugify
 from django.utils import timezone
+from django.utils.timesince import timesince
+
+
+def validate_duration(model, max_duration=timedelta(hours=24)):
+    """
+    Basic sanity checks for models with a duration
+    :param model: a model instance with 'start' and 'end' attributes
+    :param max_duration: maximum allowed duration between start and end time
+    :return:
+    """
+    if model.start and model.end:
+        if model.start > model.end:
+            raise ValidationError('Start time must come before end time')
+        if model.end - model.start > max_duration:
+            raise ValidationError('Duration too long (%(timesince)s)', params={
+                'timesince': timesince(model.start, model.end)})
 
 
 class Child(models.Model):
@@ -98,6 +117,9 @@ class Feeding(models.Model):
             self.duration = self.end - self.start
         super(Feeding, self).save(*args, **kwargs)
 
+    def clean(self):
+        validate_duration(self)
+
 
 class Note(models.Model):
     model_name = 'note'
@@ -137,6 +159,9 @@ class Sleep(models.Model):
             self.duration = self.end - self.start
         super(Sleep, self).save(*args, **kwargs)
 
+    def clean(self):
+        validate_duration(self)
+
 
 class Timer(models.Model):
     model_name = 'timer'
@@ -191,6 +216,9 @@ class Timer(models.Model):
             self.duration = None
         super(Timer, self).save(*args, **kwargs)
 
+    def clean(self):
+        validate_duration(self)
+
 
 class TummyTime(models.Model):
     model_name = 'tummytime'
@@ -213,3 +241,6 @@ class TummyTime(models.Model):
         if self.start and self.end:
             self.duration = self.end - self.start
         super(TummyTime, self).save(*args, **kwargs)
+
+    def clean(self):
+        validate_duration(self)
diff --git a/core/tests/tests_forms.py b/core/tests/tests_forms.py
index d8fe0d93..cdff19f4 100644
--- a/core/tests/tests_forms.py
+++ b/core/tests/tests_forms.py
@@ -71,6 +71,12 @@ class FormsTestCase(TestCase):
         page = self.c.post('/feedings/{}/'.format(entry.id), params)
         self.assertEqual(page.status_code, 302)
 
+        params['start'] = '2001-01-01 1:01'
+        page = self.c.post('/feedings/{}/'.format(entry.id), params)
+        self.assertEqual(page.status_code, 200)
+        self.assertFormError(page, 'form', None,
+                             'Start time must come before end time')
+
     def test_sleeping_forms(self):
         params = {
             'child': 1,
@@ -87,6 +93,12 @@ class FormsTestCase(TestCase):
         page = self.c.post('/sleep/{}/'.format(entry.id), params)
         self.assertEqual(page.status_code, 302)
 
+        params['start'] = '2001-01-01 1:01'
+        page = self.c.post('/sleep/{}/'.format(entry.id), params)
+        self.assertEqual(page.status_code, 200)
+        self.assertFormError(page, 'form', None,
+                             'Start time must come before end time')
+
     def test_timer_forms(self):
         timer = models.Timer.objects.create(user=self.user)
         timer.save()
@@ -126,3 +138,9 @@ class FormsTestCase(TestCase):
         entry = models.TummyTime.objects.first()
         page = self.c.post('/tummy-time/{}/'.format(entry.id), params)
         self.assertEqual(page.status_code, 302)
+
+        params['start'] = '2001-01-01 1:01'
+        page = self.c.post('/tummy-time/{}/'.format(entry.id), params)
+        self.assertEqual(page.status_code, 200)
+        self.assertFormError(page, 'form', None,
+                             'Start time must come before end time')