diff --git a/packages/adapter-utils/src/sandbox-callback-bridge.test.ts b/packages/adapter-utils/src/sandbox-callback-bridge.test.ts
index 2222363199..4656c27c3a 100644
--- a/packages/adapter-utils/src/sandbox-callback-bridge.test.ts
+++ b/packages/adapter-utils/src/sandbox-callback-bridge.test.ts
@@ -605,7 +605,7 @@ describe("sandbox callback bridge", () => {
         return {
           status: 200,
           headers: { "content-type": "application/json" },
-          body: JSON.stringify({ ok: true }),
+          body: Buffer.from(JSON.stringify({ ok: true }), "utf8"),
         };
       },
     });