diff --git a/src/index.ts b/src/index.ts
index 7b4cca9..48f21b4 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -57,6 +57,9 @@ export default {
     } catch {
       return json(rpcError(null, -32700, "parse error"));
     }
+    if (typeof body !== "object" || body === null || Array.isArray(body)) {
+      return json(rpcError(null, -32600, "Invalid Request"));
+    }
 
     const result = await handle(body, env, caller);
     // Notifications (no id) get a 202 with no body per JSON-RPC.
diff --git a/test/index.test.mjs b/test/index.test.mjs
index ef49ed2..eea909f 100644
--- a/test/index.test.mjs
+++ b/test/index.test.mjs
@@ -104,6 +104,26 @@ test("tools/call rejects non-object arguments", async (t) => {
   assert.equal(upstreamCalls, 0);
 });
 
+test("non-object JSON-RPC bodies get -32600 Invalid Request", async (t) => {
+  const env = {
+    BRIDGEKIT_CLIENTS: JSON.stringify({
+      "client-key": { name: "test client", tools: [], allowWrite: false },
+    }),
+  };
+
+  for (const badBody of [null, [], "foo", 42, true]) {
+    await t.test(`body ${JSON.stringify(badBody)}`, async () => {
+      const response = await mcpRequest(env, badBody);
+
+      assert.deepEqual(await response.json(), {
+        jsonrpc: "2.0",
+        id: null,
+        error: { code: -32600, message: "Invalid Request" },
+      });
+    });
+  }
+});
+
 test("/ai rejects requests without a client key before calling the model", async () => {
   let upstreamCalls = 0;
   globalThis.fetch = async () => {