diff --git a/src/hooks.ts b/src/hooks.ts
index 58a4a7b..a1a7721 100644
--- a/src/hooks.ts
+++ b/src/hooks.ts
@@ -41,13 +41,21 @@ export class AdapterHookable {
   }
 
   async upgrade(
-    request: UpgradeRequest & { context?: Peer["context"] },
+    request: UpgradeRequest & { readonly context?: Peer["context"] },
   ): Promise<{
     upgradeHeaders?: HeadersInit;
     endResponse?: Response;
     context: Peer["context"];
   }> {
-    const context = (request.context ??= {});
+    let context = request.context;
+    if (!context) {
+      context = {};
+      Object.defineProperty(request, "context", {
+        enumerable: true,
+        value: context,
+      });
+    }
+
     try {
       const res = await this.callHook(
         "upgrade",