diff --git a/PROTOCOL.md b/PROTOCOL.md
index c0196761..2b012fbb 100644
--- a/PROTOCOL.md
+++ b/PROTOCOL.md
@@ -37,7 +37,7 @@ If the server receives more than one `ConnectionInit` message at any given time,
 ```typescript
 interface ConnectionInitMessage {
   type: 'connection_init';
-  payload?: Record<string, unknown>;
+  payload?: Record<string, unknown> | null;
 }
 ```
 
@@ -52,7 +52,7 @@ The server can use the optional `payload` field to transfer additional details a
 ```typescript
 interface ConnectionAckMessage {
   type: 'connection_ack';
-  payload?: Record<string, unknown>;
+  payload?: Record<string, unknown> | null;
 }
 ```
 
@@ -73,7 +73,7 @@ The optional `payload` field can be used to transfer additional details about th
 ```typescript
 interface PingMessage {
   type: 'ping';
-  payload?: Record<string, unknown>;
+  payload?: Record<string, unknown> | null;
 }
 ```
 
@@ -90,7 +90,7 @@ The optional `payload` field can be used to transfer additional details about th
 ```typescript
 interface PongMessage {
   type: 'pong';
-  payload?: Record<string, unknown>;
+  payload?: Record<string, unknown> | null;
 }
 ```
 
diff --git a/src/__tests__/__snapshots__/common.ts.snap b/src/__tests__/__snapshots__/common.ts.snap
index 65834e7c..5047ae7a 100644
--- a/src/__tests__/__snapshots__/common.ts.snap
+++ b/src/__tests__/__snapshots__/common.ts.snap
@@ -56,13 +56,11 @@ exports[`should report invalid message {"type":""} with descriptive error 1`] =
 
 exports[`should report invalid message {"type":"complete"} with descriptive error 1`] = `""complete" message expects the 'id' property to be a string, but got undefined"`;
 
-exports[`should report invalid message {"type":"connection_ack","payload":""} with descriptive error 1`] = `""connection_ack" message expects the 'payload' property to be an object or missing, but got """`;
+exports[`should report invalid message {"type":"connection_ack","payload":""} with descriptive error 1`] = `""connection_ack" message expects the 'payload' property to be an object or nullish or missing, but got """`;
 
-exports[`should report invalid message {"type":"connection_init","payload":""} with descriptive error 1`] = `""connection_init" message expects the 'payload' property to be an object or missing, but got """`;
+exports[`should report invalid message {"type":"connection_init","payload":""} with descriptive error 1`] = `""connection_init" message expects the 'payload' property to be an object or nullish or missing, but got """`;
 
-exports[`should report invalid message {"type":"connection_init","payload":0} with descriptive error 1`] = `""connection_init" message expects the 'payload' property to be an object or missing, but got "0""`;
-
-exports[`should report invalid message {"type":"connection_init"} with descriptive error 1`] = `""connection_init" message expects the 'payload' property to be an object or missing, but got "undefined""`;
+exports[`should report invalid message {"type":"connection_init","payload":0} with descriptive error 1`] = `""connection_init" message expects the 'payload' property to be an object or nullish or missing, but got "0""`;
 
 exports[`should report invalid message {"type":"error"} with descriptive error 1`] = `""error" message expects the 'id' property to be a string, but got undefined"`;
 
@@ -72,9 +70,7 @@ exports[`should report invalid message {"type":"next"} with descriptive error 2`
 
 exports[`should report invalid message {"type":"nuxt"} with descriptive error 1`] = `"Invalid message 'type' property "nuxt""`;
 
-exports[`should report invalid message {"type":"ping","payload":0} with descriptive error 1`] = `""ping" message expects the 'payload' property to be an object or missing, but got "0""`;
-
-exports[`should report invalid message {"type":"pong"} with descriptive error 1`] = `""pong" message expects the 'payload' property to be an object or missing, but got "undefined""`;
+exports[`should report invalid message {"type":"ping","payload":0} with descriptive error 1`] = `""ping" message expects the 'payload' property to be an object or nullish or missing, but got "0""`;
 
 exports[`should report invalid message {"type":"subscribe"} with descriptive error 1`] = `""subscribe" message expects the 'id' property to be a string, but got undefined"`;
 
diff --git a/src/__tests__/common.ts b/src/__tests__/common.ts
index 222ef54f..6da157fc 100644
--- a/src/__tests__/common.ts
+++ b/src/__tests__/common.ts
@@ -36,10 +36,6 @@ it.each([
     type: MessageType.ConnectionInit,
     payload: 0,
   },
-  {
-    type: MessageType.ConnectionInit,
-    payload: undefined,
-  },
   {
     type: MessageType.ConnectionAck,
     payload: '',
@@ -48,10 +44,6 @@ it.each([
     type: MessageType.Ping,
     payload: 0,
   },
-  {
-    type: MessageType.Pong,
-    payload: undefined,
-  },
 
   // invalid subscribe message
   {
@@ -219,6 +211,10 @@ it.each([
     type: MessageType.ConnectionInit,
     payload: {},
   },
+  {
+    type: MessageType.ConnectionInit,
+    payload: null,
+  },
   {
     type: MessageType.ConnectionAck,
   },
@@ -226,6 +222,10 @@ it.each([
     type: MessageType.ConnectionAck,
     payload: {},
   },
+  {
+    type: MessageType.ConnectionAck,
+    payload: null,
+  },
   {
     type: MessageType.Ping,
   },
@@ -233,6 +233,10 @@ it.each([
     type: MessageType.Ping,
     payload: {},
   },
+  {
+    type: MessageType.Ping,
+    payload: null,
+  },
   {
     type: MessageType.Pong,
   },
@@ -240,6 +244,10 @@ it.each([
     type: MessageType.Pong,
     payload: {},
   },
+  {
+    type: MessageType.Pong,
+    payload: null,
+  },
 
   // valid subscribe message
   {
diff --git a/src/common.ts b/src/common.ts
index 7a2076a0..8987f6aa 100644
--- a/src/common.ts
+++ b/src/common.ts
@@ -228,9 +228,9 @@ export function validateMessage(val: unknown): Message {
     case MessageType.ConnectionAck:
     case MessageType.Ping:
     case MessageType.Pong: {
-      if ('payload' in val && !isObject(val.payload)) {
+      if (val.payload != null && !isObject(val.payload)) {
         throw new Error(
-          `"${val.type}" message expects the 'payload' property to be an object or missing, but got "${val.payload}"`,
+          `"${val.type}" message expects the 'payload' property to be an object or nullish or missing, but got "${val.payload}"`,
         );
       }