diff --git a/src/ui.tsx b/src/ui.tsx
index f102fe1..5ab468f 100644
--- a/src/ui.tsx
+++ b/src/ui.tsx
@@ -781,6 +781,7 @@ function LayerSelector({state}: {state: State}) {
         value={[...selectedLayers]}
         onChange={layersChanged}
         size={3}
+        disabled={state.progress != null}
       >
         {layers.map((layer) => <option key={layer}>{layer}</option>)}
       </select>