diff --git a/src/Controller/ToolsController.php b/src/Controller/ToolsController.php
index 979b2e4..2db21ab 100644
--- a/src/Controller/ToolsController.php
+++ b/src/Controller/ToolsController.php
@@ -194,6 +194,14 @@ class ToolsController extends AbstractController
                     count($cities),
                 ]);
 
+                if (empty($cities)) {
+                    throw new \RuntimeException(sprintf(
+                        'Problème improbable : les %d signalements n’ont pas pu être groupés dans les %d communes',
+                        count($issuesGeojson->getFeatures()),
+                        count($citiesOsm->elements)
+                    ));
+                }
+
                 $response->setCallback(function () use ($cities): void {
                     $headings = [
                         'name',