diff --git a/netbox/dcim/models.py b/netbox/dcim/models.py
index 0fe3bc30c..5ff233c9c 100644
--- a/netbox/dcim/models.py
+++ b/netbox/dcim/models.py
@@ -183,6 +183,16 @@ class Rack(CreatedUpdatedModel):
     def get_absolute_url(self):
         return reverse('dcim:rack', args=[self.pk])
 
+    def clean(self):
+
+        # Validate that Rack is tall enough to house the installed Devices
+        if self.pk:
+            top_device = Device.objects.filter(rack=self).order_by('-position').first()
+            min_height = top_device.position + top_device.device_type.u_height - 1
+            if self.u_height < min_height:
+                raise ValidationError("Rack must be at least {}U tall with currently installed devices."
+                                      .format(min_height))
+
     def to_csv(self):
         return ','.join([
             self.site.name,