diff --git a/biome.json b/biome.json
index 898762533..30759a3d2 100644
--- a/biome.json
+++ b/biome.json
@@ -59,6 +59,9 @@
       "correctness": {
         "useYield": "off",
         "noUnsafeFinally": "off"
+      },
+      "performance": {
+        "noDelete": "off"
       }
     }
   }
diff --git a/src/ui/side_panel.ts b/src/ui/side_panel.ts
index d41f0604f..383aaa599 100644
--- a/src/ui/side_panel.ts
+++ b/src/ui/side_panel.ts
@@ -280,7 +280,7 @@ export class SidePanelManager extends RefCounted {
   }
 
   endDrag() {
-    this.element.dataset.neuroglancerSidePanelDrag = undefined;
+    delete this.element.dataset.neuroglancerSidePanelDrag;
     this.dragSource = undefined;
   }