@@ -10,8 +10,7 @@ export default defineConfig(async config => ({
     reactRouter(),
     sentryCloudflareVitePlugin(),
     ...((await sentryReactRouter(
-      // Both Sentry plugins inject the orchestrion snippet, and injecting it twice fails the build.
-      { sourcemaps: { disable: true }, buildTimeInstrumentation: false },
+      { sourcemaps: { disable: true } },
       config,
       // eslint-disable-next-line @typescript-eslint/no-explicit-any
     )) as any[]),
 
@@ -9,17 +9,24 @@ import { resolveOrchestrionRuntimeRequest, SNIPPET_IMPORT_SPECIFIER } from './re
 
 type TransformHandler = (this: unknown, code: string, id: string, opts?: { ssr?: boolean }) => unknown;
 
+// Key of a property on the plugin object. Its value is an object that is unique to each `sentryOrchestrionPlugin()`
+// call. An SDK that wraps the plugin with an object spread (`@sentry/remix`) copies the property, so `configResolved`
+// can find the first instance in a build also through a wrapper.
+const INSTANCE_KEY = '__sentryOrchestrionInstance';
+
+type OrchestrionVitePlugin = Plugin & { [INSTANCE_KEY]?: object };
+
 // On Vite >= 6 `applyToEnvironment` (below) keeps the whole plugin out of
 // client environments. Vite 5 (e.g. Remix v2) ignores that hook, so without
 // this gate the transform would also run in the CLIENT build — where modules
 // like `@remix-run/server-runtime` sit in the client graph, and the injected
 // snippet's import of the subscriber factories (which import
 // `node:diagnostics_channel`) breaks against Vite's browser builtin shim. Gate
 // on the `ssr` flag, which Vite passes on both major versions.
-function ssrOnlyTransform(transform: Plugin['transform']): Plugin['transform'] {
+function ssrOnlyTransform(transform: Plugin['transform'], isDuplicate: () => boolean): Plugin['transform'] {
   const gate = (handler: TransformHandler): TransformHandler =>
     function (code, id, opts) {
-      if (!opts?.ssr) {
+      if (!opts?.ssr || isDuplicate()) {
         return null;
       }
       return handler.call(this, code, id, opts);
@@ -62,9 +69,14 @@ export function sentryOrchestrionPlugin(options: PluginOptions = {}): Plugin {
     '@sentry/server-utils',
   ];
 
-  return {
+  const instance = {};
+  // `true` when an earlier instance of this plugin is in the same build, which then transforms the modules alone.
+  let isDuplicate = false;
+
+  const plugin: OrchestrionVitePlugin = {
     ...upstream,
-    transform: ssrOnlyTransform(upstream.transform),
+    [INSTANCE_KEY]: instance,
+    transform: ssrOnlyTransform(upstream.transform, () => isDuplicate),
     // The module-injected snippet imports `@sentry/server-utils` from INSIDE
     // transformed `node_modules` files. Under isolated installs (pnpm) that bare
     // specifier doesn't resolve from an instrumented package's location, so when
@@ -119,8 +131,13 @@ export function sentryOrchestrionPlugin(options: PluginOptions = {}): Plugin {
       return { resolve: { noExternal: noExternalModules() } };
     },
     configResolved(config: ResolvedConfig): void {
+      // Two Sentry Vite plugins can each add this plugin to one build, for example `sentryCloudflareVitePlugin` and
+      // `sentryReactRouter`. A module transformed twice declares the injected snippet twice and fails the build.
+      const first = (config.plugins as readonly OrchestrionVitePlugin[]).find(p => p[INSTANCE_KEY]);
+      isDuplicate = first !== undefined && first[INSTANCE_KEY] !== instance;
+
       // Nothing is force-bundled in `serve`, so an externalized module is expected there.
-      if (config.command === 'serve') {
+      if (isDuplicate || config.command === 'serve') {
         return;
       }
 
@@ -140,4 +157,6 @@ export function sentryOrchestrionPlugin(options: PluginOptions = {}): Plugin {
       }
     },
   };
+
+  return plugin;
 }
@@ -227,6 +227,7 @@ describe('sentryOrchestrionPlugin (vite)', () => {
     const plugin = vitePlugin();
     (plugin.configResolved as (config: unknown) => void)({
       command,
+      plugins: [plugin],
       ssr: { external: ssrExternal },
       logger: { warn },
     } as unknown as ResolvedConfig);
@@ -324,6 +325,59 @@ describe('sentryOrchestrionPlugin (vite)', () => {
     expect(transform.call({}, 'code', 'id', { ssr: true })).toBe('transformed');
   });
 
+  it('transforms and warns only in the first instance when two Sentry plugins add it to one build', () => {
+    const first = vitePlugin();
+    const second = vitePlugin();
+    const warn = vi.fn();
+    const config = {
+      command: 'build',
+      plugins: [{ name: 'other' }, first, second],
+      ssr: { external: ['mysql'] },
+      logger: { warn },
+    } as unknown as ResolvedConfig;
+
+    (first.configResolved as (config: unknown) => void)(config);
+    (second.configResolved as (config: unknown) => void)(config);
+
+    const firstTransform = first.transform as (
+      this: unknown,
+      code: string,
+      id: string,
+      opts?: { ssr?: boolean },
+    ) => unknown;
+    const secondTransform = second.transform as (
+      this: unknown,
+      code: string,
+      id: string,
+      opts?: { ssr?: boolean },
+    ) => unknown;
+    expect(firstTransform.call({}, 'code', 'id', { ssr: true })).toBe('transformed');
+    expect(secondTransform.call({}, 'code', 'id', { ssr: true })).toBeNull();
+    expect(warn).toHaveBeenCalledTimes(1);
+  });
+
+  it('still transforms when an SDK wraps the plugin with an object spread', () => {
+    // `@sentry/remix` puts `{ ...orchestrion, configResolved, transform }` into the build and calls the original hooks.
+    const plugin = vitePlugin();
+    const wrapper = { ...plugin, configResolved: vi.fn(), transform: vi.fn() };
+    const config = {
+      command: 'build',
+      plugins: [wrapper],
+      ssr: {},
+      logger: { warn: vi.fn() },
+    } as unknown as ResolvedConfig;
+
+    (plugin.configResolved as (config: unknown) => void)(config);
+
+    const transform = plugin.transform as (
+      this: unknown,
+      code: string,
+      id: string,
+      opts?: { ssr?: boolean },
+    ) => unknown;
+    expect(transform.call({}, 'code', 'id', { ssr: true })).toBe('transformed');
+  });
+
   it('gates resolveId on the ssr flag and falls back to self-resolution', async () => {
     const plugin = vitePlugin();
     const resolveId = plugin.resolveId as (