diff --git a/packages/better-auth/src/plugins/username/index.ts b/packages/better-auth/src/plugins/username/index.ts
index 9629e3760e..96c8a6a052 100644
--- a/packages/better-auth/src/plugins/username/index.ts
+++ b/packages/better-auth/src/plugins/username/index.ts
@@ -274,7 +274,14 @@ export const username = (options?: UsernameOptions) => {
 									},
 								],
 							});
-							if (user) {
+
+							const blockChangeSignUp = ctx.path === "/sign-up/email" && user;
+							const blockChangeUpdateUser =
+								ctx.path === "/update-user" &&
+								user &&
+								ctx.context.session &&
+								user.id !== ctx.context.session.session.userId;
+							if (blockChangeSignUp || blockChangeUpdateUser) {
 								throw new APIError("UNPROCESSABLE_ENTITY", {
 									message: ERROR_CODES.USERNAME_IS_ALREADY_TAKEN,
 								});
diff --git a/packages/better-auth/src/plugins/username/username.test.ts b/packages/better-auth/src/plugins/username/username.test.ts
index 127fc102e9..9d260837a7 100644
--- a/packages/better-auth/src/plugins/username/username.test.ts
+++ b/packages/better-auth/src/plugins/username/username.test.ts
@@ -4,7 +4,7 @@ import { username } from ".";
 import { usernameClient } from "./client";
 
 describe("username", async (it) => {
-	const { client, sessionSetter } = await getTestInstance(
+	const { client, sessionSetter, signInWithTestUser } = await getTestInstance(
 		{
 			plugins: [
 				username({
@@ -70,7 +70,7 @@ describe("username", async (it) => {
 		expect(session?.user.username).toBe("new_username_2.1");
 	});
 
-	it("should fail on duplicate username", async () => {
+	it("should fail on duplicate username in sign-up", async () => {
 		const res = await client.signUp.email({
 			email: "new-email-2@gamil.com",
 			username: "New_username_2.1",
@@ -80,6 +80,45 @@ describe("username", async (it) => {
 		expect(res.error?.status).toBe(422);
 	});
 
+	it("should fail on duplicate username in update-user if user is different", async () => {
+		const newHeaders = new Headers();
+		await client.signUp.email({
+			email: "new-email-2@gamil.com",
+			username: "duplicate-username",
+			password: "new_password",
+			name: "new-name",
+			fetchOptions: {
+				headers: newHeaders,
+			},
+		});
+
+		const { headers: testUserHeaders } = await signInWithTestUser();
+		const res = await client.updateUser({
+			username: "duplicate-username",
+			fetchOptions: {
+				headers: testUserHeaders,
+			},
+		});
+		expect(res.error?.status).toBe(422);
+	});
+
+	it("should succeed on duplicate username in update-user if user is the same", async () => {
+		await client.updateUser({
+			username: "New_username_2.1",
+			fetchOptions: {
+				headers,
+			},
+		});
+
+		const session = await client.getSession({
+			fetchOptions: {
+				headers,
+				throw: true,
+			},
+		});
+		expect(session?.user.username).toBe("new_username_2.1");
+	});
+
 	it("should fail on invalid username", async () => {
 		const res = await client.signUp.email({
 			email: "email-4@email.com",