diff --git a/__tests__/create-token.test.ts b/__tests__/create-token.test.ts
index 5a25dc4..2fb65d4 100644
--- a/__tests__/create-token.test.ts
+++ b/__tests__/create-token.test.ts
@@ -58,6 +58,26 @@ describe('creating tokens', () => {
       }
     });
 
+    it('should not encode validity_in_seconds in the payload', () => {
+      const token = client.generateUserToken({
+        user_id: userId,
+        validity_in_seconds: 120,
+      });
+      const decodedToken = jwt.verify(token, secret) as any;
+
+      expect(decodedToken).not.toHaveProperty('validity_in_seconds');
+      expect(Object.keys(decodedToken).sort()).toEqual(
+        ['exp', 'iat', 'user_id'].sort(),
+      );
+    });
+
+    it('should not mutate the provided payload', () => {
+      const payload = { user_id: userId, validity_in_seconds: 120 };
+      client.generateUserToken(payload);
+
+      expect(payload).toEqual({ user_id: userId, validity_in_seconds: 120 });
+    });
+
     it(`should make sure iat is correct`, () => {
       for (let i = 0; i < 5; i++) {
         const token = client.generateUserToken({ user_id: userId });
@@ -118,6 +138,18 @@ describe('creating tokens', () => {
       expect(decodedToken.exp).toBeDefined();
     });
 
+    it('should not encode validity_in_seconds in the payload', () => {
+      const token = client.generateCallToken({
+        user_id: userId,
+        call_cids,
+        validity_in_seconds: 120,
+      });
+      const decodedToken = jwt.verify(token, secret) as any;
+
+      expect(decodedToken).not.toHaveProperty('validity_in_seconds');
+      expect(decodedToken.exp - decodedToken.iat).toBe(120);
+    });
+
     it('with default expiration', () => {
       for (let i = 0; i < 5; i++) {
         const token = client.generateCallToken({ user_id: userId, call_cids });
diff --git a/src/StreamClient.ts b/src/StreamClient.ts
index 1cd8efb..f38ac43 100644
--- a/src/StreamClient.ts
+++ b/src/StreamClient.ts
@@ -133,12 +133,17 @@ export class StreamClient extends CommonApi {
       iat?: number;
     } & Record<string, unknown>,
   ) => {
+    // validity_in_seconds is only used to compute exp, don't encode it
+    const { validity_in_seconds, ...claims } = payload;
     const defaultIat = Math.floor((Date.now() - 1000) / 1000);
-    payload.iat = payload.iat ?? defaultIat;
-    const validityInSeconds = payload.validity_in_seconds ?? 60 * 60;
-    payload.exp = payload.exp ?? payload.iat + validityInSeconds;
+    const iat = claims.iat ?? defaultIat;
+    const exp = claims.exp ?? iat + (validity_in_seconds ?? 60 * 60);
 
-    return JWTUserToken(this.secret, payload as UserTokenPayload);
+    return JWTUserToken(this.secret, {
+      ...claims,
+      iat,
+      exp,
+    } as UserTokenPayload);
   };
 
   /**
@@ -154,9 +159,11 @@ export class StreamClient extends CommonApi {
     } & Record<string, unknown>,
   ) => {
     const defaultIat = Math.floor((Date.now() - 1000) / 1000);
-    payload.iat = payload.iat ?? defaultIat;
 
-    return JWTUserToken(this.secret, payload as UserTokenPayload);
+    return JWTUserToken(this.secret, {
+      ...payload,
+      iat: payload.iat ?? defaultIat,
+    } as UserTokenPayload);
   };
 
   /**