diff --git a/.changeset/cloudflare-respect-custom-image-service.md b/.changeset/cloudflare-respect-custom-image-service.md
new file mode 100644
index 000000000000..c5f882aee35a
--- /dev/null
+++ b/.changeset/cloudflare-respect-custom-image-service.md
@@ -0,0 +1,7 @@
+---
+'@astrojs/cloudflare': patch
+---
+
+Preserve user-defined image services when the Cloudflare adapter is used. Previously, the adapter's `imageService` mode (including the default `'cloudflare-binding'` and `'compile'`) would silently overwrite a custom `image.service` configured in `astro.config.*`, replacing it with the workerd image service. Custom services (e.g., third-party CDNs) are now preserved across all modes, matching the behavior of the explicit `'custom'` mode.
+
+Additionally, the workerd prerenderer no longer hard-swaps `globalThis.astroAsset.imageService` to `astro/assets/services/sharp` for byte-level static image generation when a custom service is in use. Previously the `'compile'` mode bypassed the preserved service during the Node-side image generation pass; it now uses the user's configured service throughout the build.
diff --git a/packages/integrations/cloudflare/src/index.ts b/packages/integrations/cloudflare/src/index.ts
index d006b312ec24..e75199c26058 100644
--- a/packages/integrations/cloudflare/src/index.ts
+++ b/packages/integrations/cloudflare/src/index.ts
@@ -123,6 +123,11 @@ export default function createIntegration({
 	let _routes: IntegrationResolvedRoute[];
 	let _isFullyStatic = false;
 	let cfPluginConfig: PluginConfig;
+	// True when the user provided a non-default `image.service`, which `setImageConfig`
+	// preserves across all `imageService` modes. In that case the workerd stub never
+	// becomes the active service, so the Node-side `collectStaticImages` path (which
+	// hard-swaps to sharp) must not run — it would clobber the user's service.
+	let _hasCustomImageService = false;
 
 	const { buildService, runtimeService } = normalizeImageServiceConfig(imageService);
 	const needsImagesBinding = runtimeService === 'cloudflare-binding';
@@ -135,6 +140,11 @@ export default function createIntegration({
 					throw new Error('`workerd` does not run on Stackblitz.');
 				}
 
+				// Read this from the user's pre-`updateConfig` image config, since
+				// `setImageConfig` below may replace `service` with the workerd stub.
+				_hasCustomImageService =
+					config.image.service.entrypoint !== 'astro/assets/services/sharp';
+
 				let session = config.session;
 				const isCompile = buildService === 'compile';
 
@@ -417,7 +427,7 @@ export default function createIntegration({
 							base: _config.base,
 							trailingSlash: _config.trailingSlash,
 							cfPluginConfig,
-							hasCompileImageService: buildService === 'compile',
+							hasCompileImageService: buildService === 'compile' && !_hasCustomImageService,
 						}),
 					);
 				}
diff --git a/packages/integrations/cloudflare/src/utils/image-config.ts b/packages/integrations/cloudflare/src/utils/image-config.ts
index 473bd6993718..0d28b158e0f8 100644
--- a/packages/integrations/cloudflare/src/utils/image-config.ts
+++ b/packages/integrations/cloudflare/src/utils/image-config.ts
@@ -56,6 +56,19 @@ export function setImageConfig(
 ) {
 	const { buildService, runtimeService } = normalizeImageServiceConfig(service);
 
+	// If the user has configured a non-default image service, preserve it across
+	// all `imageService` modes. This matches the explicit `'custom'` mode and the
+	// fallback branch below, and prevents the adapter from silently overriding a
+	// user-defined service (e.g., a third-party CDN) when the default mode is in
+	// effect or `'compile'`/`'cloudflare-binding'` is selected.
+	const hasCustomService = config.service.entrypoint !== 'astro/assets/services/sharp';
+	if (hasCustomService && buildService !== 'custom') {
+		logger.info(
+			`Detected a custom image service (${config.service.entrypoint}). Preserving it instead of applying the '${buildService}' mode override. Set \`imageService: 'custom'\` to silence this notice.`,
+		);
+		return { ...config };
+	}
+
 	switch (buildService) {
 		case 'passthrough':
 			return {
diff --git a/packages/integrations/cloudflare/test/image-config.test.ts b/packages/integrations/cloudflare/test/image-config.test.ts
new file mode 100644
index 000000000000..5913fa2e52b2
--- /dev/null
+++ b/packages/integrations/cloudflare/test/image-config.test.ts
@@ -0,0 +1,74 @@
+import * as assert from 'node:assert/strict';
+import { describe, it } from 'node:test';
+import type { AstroConfig, AstroIntegrationLogger } from 'astro';
+import { setImageConfig } from '../src/utils/image-config.ts';
+
+const SHARP_ENTRYPOINT = 'astro/assets/services/sharp';
+const CUSTOM_ENTRYPOINT = 'my-app/image-services/cdn';
+const WORKERD_ENTRYPOINT = '@astrojs/cloudflare/image-service-workerd';
+
+function createNoopLogger(): AstroIntegrationLogger {
+	const noop = () => {};
+	const logger = {
+		options: {} as never,
+		label: 'test',
+		fork: () => logger,
+		info: noop,
+		warn: noop,
+		error: noop,
+		debug: noop,
+	};
+	return logger as unknown as AstroIntegrationLogger;
+}
+
+function makeConfig(entrypoint: string): AstroConfig['image'] {
+	return { service: { entrypoint, config: {} } } as AstroConfig['image'];
+}
+
+describe('setImageConfig — custom image service preservation', () => {
+	for (const mode of [
+		undefined, // default → 'cloudflare-binding'
+		'passthrough',
+		'cloudflare',
+		'cloudflare-binding',
+		'compile',
+		{ build: 'compile' as const },
+		{ build: 'compile' as const, runtime: 'cloudflare-binding' as const },
+	]) {
+		it(`preserves a user-defined service when imageService = ${JSON.stringify(mode)}`, () => {
+			const customConfig = makeConfig(CUSTOM_ENTRYPOINT);
+			const result = setImageConfig(mode as any, customConfig, 'build', createNoopLogger());
+			assert.equal(
+				result.service.entrypoint,
+				CUSTOM_ENTRYPOINT,
+				`Expected custom service to be preserved for mode ${JSON.stringify(mode)}`,
+			);
+		});
+	}
+
+	it("does not preserve when user has the default sharp service (mode 'cloudflare-binding')", () => {
+		const sharpConfig = makeConfig(SHARP_ENTRYPOINT);
+		const result = setImageConfig('cloudflare-binding', sharpConfig, 'build', createNoopLogger());
+		assert.equal(
+			result.service.entrypoint,
+			WORKERD_ENTRYPOINT,
+			'Expected adapter to override default sharp for cloudflare-binding mode',
+		);
+	});
+
+	it("does not preserve when user has the default sharp service (mode 'compile')", () => {
+		const sharpConfig = makeConfig(SHARP_ENTRYPOINT);
+		const result = setImageConfig('compile', sharpConfig, 'build', createNoopLogger());
+		assert.equal(
+			result.service.entrypoint,
+			WORKERD_ENTRYPOINT,
+			'Expected adapter to override default sharp for compile mode',
+		);
+	});
+
+	it("respects an explicit 'custom' mode regardless of service", () => {
+		const customConfig = makeConfig(CUSTOM_ENTRYPOINT);
+		const result = setImageConfig('custom', customConfig, 'build', createNoopLogger());
+		assert.equal(result.service.entrypoint, CUSTOM_ENTRYPOINT);
+	});
+});