diff --git a/app/Http/Controllers/SystemController.php b/app/Http/Controllers/SystemController.php
index 307f637..636ae4c 100644
--- a/app/Http/Controllers/SystemController.php
+++ b/app/Http/Controllers/SystemController.php
@@ -528,6 +528,18 @@ class SystemController extends Controller
 		$this->authorize('admin',$o);
 		session()->flash('accordion','address');
 
+		// Make sure that no other system has this address active.
+		if (! $o->active && ($x=Address::where([
+				'zone_id'=>$o->zone_id,
+				'host_id'=>$o->host_id,
+				'node_id'=>$o->node_id,
+				'point_id'=>$o->point_id,
+				'active'=>TRUE,
+			])->single())) {
+
+			return redirect()->back()->withErrors(['susaddress'=>sprintf('%s is already active on system [<a href="%s">%s</a>]',$o->ftn,url('ftn/system/addedit',$x->system_id),$x->system->name)]);
+		}
+
 		$o->active = (! $o->active);
 		$o->save();
 
diff --git a/resources/views/system/addedit.blade.php b/resources/views/system/addedit.blade.php
index 9b476b9..9c06670 100644
--- a/resources/views/system/addedit.blade.php
+++ b/resources/views/system/addedit.blade.php
@@ -131,6 +131,12 @@
 								@endforeach
 								</tbody>
 							</table>
+
+							@error('susaddress')
+								<span class="btn btn-sm btn-danger" role="alert" style="text-align: left;">
+									{!! $message !!}
+								</span>
+							@enderror
 						@endif
 
 						@can('admin',$o)
@@ -388,6 +394,13 @@
 	@include('widgets.modal_purge')
 @endsection
 
+@section('page-css')
+	<style>
+		span.btn.btn-danger a {
+			color: white
+		}
+	</style>
+@endsection
 @section('page-scripts')
 	<script type="text/javascript">
 		$(document).ready(function() {