diff --git a/package-lock.json b/package-lock.json
index 50f492b4..4f8d9d58 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "@replit/river",
-  "version": "0.207.0",
+  "version": "0.207.1",
   "lockfileVersion": 2,
   "requires": true,
   "packages": {
     "": {
       "name": "@replit/river",
-      "version": "0.207.0",
+      "version": "0.207.1",
       "license": "MIT",
       "dependencies": {
         "@msgpack/msgpack": "^3.0.0-beta2",
diff --git a/package.json b/package.json
index 1f47db2c..17dba475 100644
--- a/package.json
+++ b/package.json
@@ -1,7 +1,7 @@
 {
   "name": "@replit/river",
   "description": "It's like tRPC but... with JSON Schema Support, duplex streaming and support for service multiplexing. Transport agnostic!",
-  "version": "0.207.0",
+  "version": "0.207.1",
   "type": "module",
   "exports": {
     ".": {
diff --git a/transport/sessionStateMachine/SessionConnected.ts b/transport/sessionStateMachine/SessionConnected.ts
index f224585f..60fc90e8 100644
--- a/transport/sessionStateMachine/SessionConnected.ts
+++ b/transport/sessionStateMachine/SessionConnected.ts
@@ -226,7 +226,13 @@ export class SessionConnected<
     // if we are not actively heartbeating, we are in passive
     // heartbeat mode and should send a response to the ack
     if (!this.isActivelyHeartbeating) {
-      this.sendHeartbeat();
+      // purposefully make this async to avoid weird browser behavior
+      // where _some_ browsers will decide that it is ok to interrupt fully
+      // synchronous code execution (e.g. an existing .send) to receive a
+      // websocket message and hit this codepath
+      void Promise.resolve().then(() => {
+        this.sendHeartbeat();
+      });
     }
   };
 
diff --git a/transport/sessionStateMachine/common.ts b/transport/sessionStateMachine/common.ts
index 8a53d981..cfbbebc8 100644
--- a/transport/sessionStateMachine/common.ts
+++ b/transport/sessionStateMachine/common.ts
@@ -281,6 +281,10 @@ export abstract class IdentifiedSession extends CommonSession {
   constructMsg<Payload>(
     partialMsg: PartialTransportMessage<Payload>,
   ): TransportMessage<Payload> {
+    if (this._isConsumed) {
+      throw new Error(ERR_CONSUMED);
+    }
+
     const msg = {
       ...partialMsg,
       id: generateId(),
diff --git a/transport/sessionStateMachine/stateMachine.test.ts b/transport/sessionStateMachine/stateMachine.test.ts
index 1792d000..894f41ab 100644
--- a/transport/sessionStateMachine/stateMachine.test.ts
+++ b/transport/sessionStateMachine/stateMachine.test.ts
@@ -1958,7 +1958,9 @@ describe('session state machine', () => {
       );
 
       // make sure the session acks the heartbeat
-      expect(conn.send).toHaveBeenCalledTimes(1);
+      await waitFor(() => {
+        expect(conn.send).toHaveBeenCalledTimes(1);
+      });
     });
 
     test('does not dispatch acks', async () => {