diff --git a/tests/jest.setup.ts b/tests/jest.setup.ts
index f677ecc..26e590c 100644
--- a/tests/jest.setup.ts
+++ b/tests/jest.setup.ts
@@ -1,5 +1,9 @@
 process.env.NODE_ENV = 'test';
 process.env.MONGOMS_DOWNLOAD_PROGRESS = '0';
+// Pin the MongoDB binary used by mongodb-memory-server. Without this, the
+// default (6.0.x) is downloaded on first run. A value set in the environment
+// still takes precedence so CI can override it.
+process.env.MONGOMS_VERSION = process.env.MONGOMS_VERSION ?? '7.0.14';
 // The env schema requires a >=16 char JWT secret and tests sign tokens with
 // this exact value. dotenv does not override real environment variables, so
 // this only applies when the runner does not provide a usable secret (a