diff --git a/src/camera.js b/src/camera.js
index cf20f73..3fddf9f 100644
--- a/src/camera.js
+++ b/src/camera.js
@@ -67,8 +67,11 @@ export function grabFrame(videoElement, maxEdge = 1280) {
 /** Ersatzweg ohne Kamera: Bilddatei auswaehlen (z. B. am Rechner). */
 export async function imageDataFromFile(file, maxEdge = 1280) {
   const bitmap = await createImageBitmap(file);
-  assertHasSize(bitmap.width, bitmap.height);
-  const data = drawScaled(bitmap, bitmap.width, bitmap.height, maxEdge);
-  bitmap.close();
-  return data;
+  try {
+    assertHasSize(bitmap.width, bitmap.height);
+    const data = drawScaled(bitmap, bitmap.width, bitmap.height, maxEdge);
+    return data;
+  } finally {
+    bitmap.close();
+  }
 }