diff --git a/app/assets/javascripts/admin/components/screened-ip-address-form.js.es6 b/app/assets/javascripts/admin/components/screened-ip-address-form.js.es6
index 0f8a29ba8c3..ef6e7596d11 100644
--- a/app/assets/javascripts/admin/components/screened-ip-address-form.js.es6
+++ b/app/assets/javascripts/admin/components/screened-ip-address-form.js.es6
@@ -48,13 +48,17 @@ export default Ember.Component.extend({
           action_name: this.get('actionName')
         });
         screenedIpAddress.save().then(result => {
-          this.setProperties({ ip_address: '', formSubmitted: false });
-          this.sendAction('action', ScreenedIpAddress.create(result.screened_ip_address));
-          Ember.run.schedule('afterRender', () => this.$('.ip-address-input').focus());
+          if (result.success) {
+            this.setProperties({ ip_address: '', formSubmitted: false });
+            this.sendAction('action', ScreenedIpAddress.create(result.screened_ip_address));
+            Ember.run.schedule('afterRender', () => this.$('.ip-address-input').focus());
+          } else {
+            bootbox.alert(result.errors);
+          }
         }).catch(e => {
           this.set('formSubmitted', false);
-          const msg = (e.responseJSON && e.responseJSON.errors) ?
-                      I18n.t("generic_error_with_reason", {error: e.responseJSON.errors.join('. ')}) :
+          const msg = (e.jqXHR.responseJSON && e.jqXHR.responseJSON.errors) ?
+                      I18n.t("generic_error_with_reason", {error: e.jqXHR.responseJSON.errors.join('. ')}) :
                       I18n.t("generic_error");
           bootbox.alert(msg, () => this.$('.ip-address-input').focus());
         });
diff --git a/app/models/screened_ip_address.rb b/app/models/screened_ip_address.rb
index f0e51ab0456..60871eaba43 100644
--- a/app/models/screened_ip_address.rb
+++ b/app/models/screened_ip_address.rb
@@ -10,11 +10,21 @@ class ScreenedIpAddress < ActiveRecord::Base
   default_action :block
 
   validates :ip_address, ip_address_format: true, presence: true
+  after_validation :check_for_match
 
   def self.watch(ip_address, opts = {})
     match_for_ip_address(ip_address) || create(opts.slice(:action_type).merge(ip_address: ip_address))
   end
 
+  def check_for_match
+    unless self.errors[:ip_address].present?
+      matched = self.class.match_for_ip_address(self.ip_address)
+      if matched && matched.action_type == self.action_type
+        self.errors.add(:ip_address, :ip_address_already_screened)
+      end
+    end
+  end
+
   # In Rails 4.0.0, validators are run to handle invalid assignments to inet columns (as they should).
   # In Rails 4.0.1, an exception is raised before validation happens, so we need this hack for
   # inet/cidr columns:
diff --git a/config/locales/server.en.yml b/config/locales/server.en.yml
index 47135628c88..52fd114f69d 100644
--- a/config/locales/server.en.yml
+++ b/config/locales/server.en.yml
@@ -132,6 +132,7 @@ en:
       odd: must be odd
       record_invalid: ! 'Validation failed: %{errors}'
       max_emojis: "can't have more than %{max_emojis_count} emoji"
+      ip_address_already_screened: "is already included in an existing rule"
       restrict_dependent_destroy:
         one: "Cannot delete record because a dependent %{record} exists"
         many: "Cannot delete record because dependent %{record} exist"
diff --git a/spec/models/screened_ip_address_spec.rb b/spec/models/screened_ip_address_spec.rb
index 6210f832b0d..2b8a8d82f80 100644
--- a/spec/models/screened_ip_address_spec.rb
+++ b/spec/models/screened_ip_address_spec.rb
@@ -31,6 +31,13 @@ describe ScreenedIpAddress do
         described_class.new(valid_params.merge(action_name: nil))
       }.to raise_error(ArgumentError)
     end
+
+    it 'returns a useful error if ip address matches an existing record' do
+      ScreenedIpAddress.create(ip_address: '2600:387:b:f::7a/128', action_name: :block)
+      r = ScreenedIpAddress.new(ip_address: '2600:387:b:f::7a', action_name: :block)
+      expect(r.save).to eq(false)
+      expect(r.errors[:ip_address]).to be_present
+    end
   end
 
   describe "ip_address_with_mask" do