diff --git a/netbox/ipam/forms.py b/netbox/ipam/forms.py
index ba0d02584..83be76169 100644
--- a/netbox/ipam/forms.py
+++ b/netbox/ipam/forms.py
@@ -346,20 +346,54 @@ class IPAddressBulkAddForm(BootstrapMixin, forms.Form):
 
 
 class IPAddressAssignForm(BootstrapMixin, forms.Form):
-    site = forms.ModelChoiceField(queryset=Site.objects.all(), label='Site', required=False,
-                                  widget=forms.Select(attrs={'filter-for': 'rack'}))
-    rack = forms.ModelChoiceField(queryset=Rack.objects.all(), label='Rack', required=False,
-                                  widget=APISelect(api_url='/api/dcim/racks/?site_id={{site}}',
-                                                   display_field='display_name', attrs={'filter-for': 'device'}))
-    device = forms.ModelChoiceField(queryset=Device.objects.all(), label='Device', required=False,
-                                    widget=APISelect(api_url='/api/dcim/devices/?rack_id={{rack}}',
-                                                     display_field='display_name', attrs={'filter-for': 'interface'}))
-    livesearch = forms.CharField(required=False, label='Device', widget=Livesearch(
-        query_key='q', query_url='dcim-api:device_list', field_to_update='device')
+    site = forms.ModelChoiceField(
+        queryset=Site.objects.all(),
+        label='Site',
+        required=False,
+        widget=forms.Select(
+            attrs={'filter-for': 'rack'}
+        )
+    )
+    rack = forms.ModelChoiceField(
+        queryset=Rack.objects.all(),
+        label='Rack',
+        required=False,
+        widget=APISelect(
+            api_url='/api/dcim/racks/?site_id={{site}}',
+            display_field='display_name',
+            attrs={'filter-for': 'device', 'nullable': 'true'}
+        )
+    )
+    device = forms.ModelChoiceField(
+        queryset=Device.objects.all(),
+        label='Device',
+        required=False,
+        widget=APISelect(
+            api_url='/api/dcim/devices/?site_id={{site}}&rack_id={{rack}}',
+            display_field='display_name',
+            attrs={'filter-for': 'interface'}
+        )
+    )
+    livesearch = forms.CharField(
+        required=False,
+        label='Device',
+        widget=Livesearch(
+            query_key='q',
+            query_url='dcim-api:device_list',
+            field_to_update='device'
+        )
+    )
+    interface = forms.ModelChoiceField(
+        queryset=Interface.objects.all(),
+        label='Interface',
+        widget=APISelect(
+            api_url='/api/dcim/devices/{{device}}/interfaces/'
+        )
+    )
+    set_as_primary = forms.BooleanField(
+        label='Set as primary IP for device',
+        required=False
     )
-    interface = forms.ModelChoiceField(queryset=Interface.objects.all(), label='Interface',
-                                       widget=APISelect(api_url='/api/dcim/devices/{{device}}/interfaces/'))
-    set_as_primary = forms.BooleanField(label='Set as primary IP for device', required=False)
 
     def __init__(self, *args, **kwargs):
 
diff --git a/netbox/ipam/views.py b/netbox/ipam/views.py
index b53bb82ab..191d33a90 100644
--- a/netbox/ipam/views.py
+++ b/netbox/ipam/views.py
@@ -559,6 +559,8 @@ def ipaddress_assign(request, pk):
                 device.save()
 
             return redirect('ipam:ipaddress', pk=ipaddress.pk)
+        else:
+            assert False, form.errors
 
     else:
         form = forms.IPAddressAssignForm()
diff --git a/netbox/project-static/js/forms.js b/netbox/project-static/js/forms.js
index c86a33fcc..e421f6283 100644
--- a/netbox/project-static/js/forms.js
+++ b/netbox/project-static/js/forms.js
@@ -77,11 +77,7 @@ $(document).ready(function() {
 
         // Wipe out any existing options within the child field and create a default option
         child_field.empty();
-        var default_option = $("<option></option>").attr("value", "").text("---------");
-        if (child_field.attr('nullable') == 'true') {
-            default_option.attr("value", "0");
-        }
-        child_field.append(default_option);
+        child_field.append($("<option></option>").attr("value", "").text("---------"));
 
         if ($(this).val() || $(this).attr('nullable') == 'true') {
             var api_url = child_field.attr('api-url');
@@ -96,7 +92,7 @@ $(document).ready(function() {
                 var filter_field = $('#id_' + match[1]);
                 if (filter_field.val()) {
                     api_url = api_url.replace(match[0], filter_field.val());
-                } else {
+                } else if ($(this).attr('nullable') == 'true') {
                     api_url = api_url.replace(match[0], '0');
                 }
             }