diff --git a/packages/mongodb-memory-server-core/src/util/MongoBinaryDownloadUrl.ts b/packages/mongodb-memory-server-core/src/util/MongoBinaryDownloadUrl.ts
index 7c59488b1..3fcc17b5d 100644
--- a/packages/mongodb-memory-server-core/src/util/MongoBinaryDownloadUrl.ts
+++ b/packages/mongodb-memory-server-core/src/util/MongoBinaryDownloadUrl.ts
@@ -289,6 +289,8 @@ export class MongoBinaryDownloadUrl implements MongoBinaryDownloadUrlOpts {
       throw new UnknownVersionError(this.version);
     }
 
+    // without any "release"(empty string), fallback to testing
+    // see https://tracker.debian.org/news/1433360/accepted-base-files-13-source-into-unstable/
     const isTesting = ['unstable', 'testing', ''].includes(os.release);
 
     if (isTesting || release >= 11) {