diff --git a/src/jwt-model.ts b/src/jwt-model.ts
index f4db0fc..1b67d9a 100644
--- a/src/jwt-model.ts
+++ b/src/jwt-model.ts
@@ -21,6 +21,7 @@ export type JwtHeader = JwtHeaderStandardFields & JsonObject;
 interface JwtPayloadStandardFields {
   exp?: number; // expires: https://tools.ietf.org/html/rfc7519#section-4.1.4
   iss?: string; // issuer: https://tools.ietf.org/html/rfc7519#section-4.1.1
+  sub?: string; // subject: https://tools.ietf.org/html/rfc7519#section-4.1.2
   aud?: string | string[]; // audience: https://tools.ietf.org/html/rfc7519#section-4.1.3
   nbf?: number; // not before: https://tools.ietf.org/html/rfc7519#section-4.1.5
   iat?: number; // issued at: https://tools.ietf.org/html/rfc7519#section-4.1.6
diff --git a/src/jwt.ts b/src/jwt.ts
index 9fbfb07..895a1ed 100644
--- a/src/jwt.ts
+++ b/src/jwt.ts
@@ -58,6 +58,9 @@ function assertJwtPayload(
   if (payload.iss !== undefined && typeof payload.iss !== "string") {
     throw new JwtParseError("JWT payload iss claim is not a string");
   }
+  if (payload.sub !== undefined && typeof payload.sub !== "string") {
+    throw new JwtParseError("JWT payload sub claim is not a string");
+  }
   if (
     payload.aud !== undefined &&
     typeof payload.aud !== "string" &&
diff --git a/tests/unit/jwt-rsa.test.ts b/tests/unit/jwt-rsa.test.ts
index 96eb4dc..2c17f6c 100644
--- a/tests/unit/jwt-rsa.test.ts
+++ b/tests/unit/jwt-rsa.test.ts
@@ -430,6 +430,18 @@ describe("unit tests jwt verifier", () => {
         expect(statement).toThrow("JWT payload iss claim is not a string");
         expect(statement).toThrow(JwtParseError);
       });
+      test("JWT with sub that is not a string", () => {
+        const header = base64url('{"alg":"RS256"}');
+        const payload = base64url('{"sub":12345}');
+        const signedJwt = `${header}.${payload}.signature`;
+        const statement = () =>
+          verifyJwtSync(signedJwt, keypair.jwk, {
+            audience: null,
+            issuer: null,
+          });
+        expect(statement).toThrow("JWT payload sub claim is not a string");
+        expect(statement).toThrow(JwtParseError);
+      });
       test("JWT with aud that is not a string", () => {
         const header = base64url('{"alg":"RS256"}');
         const payload = base64url('{"aud":12345}');