diff --git a/packages/hono/src/bun/sdk.ts b/packages/hono/src/bun/sdk.ts
index d30269058f4d..892b7535bca6 100644
--- a/packages/hono/src/bun/sdk.ts
+++ b/packages/hono/src/bun/sdk.ts
@@ -1,5 +1,5 @@
 import type { Client } from '@sentry/core';
-import { applySdkMetadata } from '@sentry/core';
+import { applySdkMetadata, consoleSandbox, getClient } from '@sentry/core';
 import { init as initBun } from '@sentry/bun';
 import type { HonoBunOptions } from './middleware';
 import { buildFilteredIntegrations } from '../shared/buildFilteredIntegrations';
@@ -12,6 +12,15 @@ import { buildFilteredIntegrations } from '../shared/buildFilteredIntegrations';
  * When manually calling `init`, add the `honoIntegration` to the `integrations` array to set up the Hono integration.
  */
 export function init(options: HonoBunOptions): Client | undefined {
+  if (getClient()) {
+    consoleSandbox(() => {
+      // eslint-disable-next-line no-console
+      console.warn(
+        '[Sentry] Sentry is already initialized. Sentry should only be initialized once, through the `sentry()` middleware. Remove the `Sentry.init()` call, if one exists.',
+      );
+    });
+  }
+
   applySdkMetadata(options, 'hono', ['hono', 'bun']);
 
   // Remove Hono from the SDK defaults to prevent double instrumentation: @sentry/bun
diff --git a/packages/hono/test/bun/middleware.test.ts b/packages/hono/test/bun/middleware.test.ts
index 8e3135e52afb..0506a211e06e 100644
--- a/packages/hono/test/bun/middleware.test.ts
+++ b/packages/hono/test/bun/middleware.test.ts
@@ -3,6 +3,7 @@ import { SDK_VERSION } from '@sentry/core';
 import { Hono } from 'hono';
 import { beforeEach, describe, expect, it, type Mock, vi } from 'vitest';
 import { sentry } from '../../src/bun/middleware';
+import { init } from '../../src/bun/sdk';
 
 vi.mock('@sentry/bun', () => ({
   init: vi.fn(),
@@ -18,10 +19,14 @@ vi.mock('@sentry/core', async () => {
     // eslint-disable-next-line @typescript-eslint/ban-ts-comment
     // @ts-ignore
     applySdkMetadata: vi.fn(actual.applySdkMetadata),
+    getClient: vi.fn(() => undefined),
+    // Pass-through so console.warn calls inside consoleSandbox are observable in tests
+    consoleSandbox: vi.fn((cb: () => unknown) => cb()),
   };
 });
 
 const applySdkMetadataMock = SentryCore.applySdkMetadata as Mock;
+const getClientMock = SentryCore.getClient as Mock;
 
 describe('Hono Bun Middleware', () => {
   beforeEach(() => {
@@ -51,7 +56,8 @@ describe('Hono Bun Middleware', () => {
       expect(applySdkMetadataMock).toHaveBeenCalledWith(options, 'hono', ['hono', 'bun']);
     });
 
-    it('calls init from @sentry/bun', () => {
+    it('calls init from @sentry/bun when no client exists yet', () => {
+      getClientMock.mockReturnValue(undefined);
       const app = new Hono();
       const options = {
         dsn: 'https://public@dsn.ingest.sentry.io/1337',
@@ -156,4 +162,47 @@ describe('Hono Bun Middleware', () => {
       );
     });
   });
+
+  describe('double-init guard', () => {
+    it('still calls init even when Sentry is already initialized', () => {
+      const fakeClient = { getOptions: () => ({}) };
+      getClientMock.mockReturnValue(fakeClient as unknown as SentryCore.Client);
+
+      const app = new Hono();
+      sentry(app, { dsn: 'https://public@dsn.ingest.sentry.io/1337' });
+
+      expect(initBunMock).toHaveBeenCalledTimes(1);
+    });
+
+    it('emits a console.warn directing to remove the duplicate init call when Sentry is already initialized', () => {
+      const warnSpy = vi.spyOn(console, 'warn');
+      const fakeClient = { getOptions: () => ({}) };
+      getClientMock.mockReturnValue(fakeClient as unknown as SentryCore.Client);
+
+      const app = new Hono();
+      sentry(app, { dsn: 'https://public@dsn.ingest.sentry.io/1337' });
+
+      expect(warnSpy).toHaveBeenCalledTimes(1);
+      expect(warnSpy).toHaveBeenCalledWith(expect.stringContaining('Sentry is already initialized'));
+      expect(warnSpy).toHaveBeenCalledWith(expect.stringContaining('Remove the `Sentry.init()` call'));
+    });
+
+    it('does not emit a console.warn when no client exists yet', () => {
+      const warnSpy = vi.spyOn(console, 'warn');
+      getClientMock.mockReturnValue(undefined);
+
+      const app = new Hono();
+      sentry(app, { dsn: 'https://public@dsn.ingest.sentry.io/1337' });
+
+      expect(warnSpy).not.toHaveBeenCalled();
+    });
+
+    it('always calls init regardless of whether a client already exists', () => {
+      getClientMock.mockReturnValue(undefined);
+
+      init({ dsn: 'https://public@dsn.ingest.sentry.io/1337' });
+
+      expect(initBunMock).toHaveBeenCalledTimes(1);
+    });
+  });
 });