diff --git a/web_dialog_size/static/src/js/web_dialog_size.esm.js b/web_dialog_size/static/src/js/web_dialog_size.esm.js
index 93b646c79c2c..ad097cc83e1d 100644
--- a/web_dialog_size/static/src/js/web_dialog_size.esm.js
+++ b/web_dialog_size/static/src/js/web_dialog_size.esm.js
@@ -18,11 +18,15 @@ export class ExpandButton extends Component {
 
         onMounted(() => {
             var self = this;
-            this.config.then(function (r) {
-                if (r.default_maximize && stop) {
-                    self.dialog_button_extend();
-                }
-            });
+            this.config
+                .then(function (r) {
+                    if (r.default_maximize && stop) {
+                        self.dialog_button_extend();
+                    }
+                })
+                .catch(() => {
+                    // Session likely expired → ignore
+                });
         });
     }