diff --git a/packages/cli/src/utils.ts b/packages/cli/src/utils.ts
index d8a567a230..b1a4d1b649 100644
--- a/packages/cli/src/utils.ts
+++ b/packages/cli/src/utils.ts
@@ -1,4 +1,12 @@
-import { ApiKeyResponseDto, getMyApiKey, getMyUser, init, isHttpError, Permission } from '@immich/sdk';
+import {
+  ApiKeyResponseDto,
+  getMyApiKey,
+  getMyUser,
+  init,
+  isHttpError,
+  isMalformedResponseError,
+  Permission,
+} from '@immich/sdk';
 import { convertPathToPattern, glob } from 'fast-glob';
 import { createHash } from 'node:crypto';
 import { createReadStream } from 'node:fs';
@@ -82,7 +90,7 @@ export const connect = async (url: string, key: string) => {
   init({ baseUrl: url, apiKey: key });
 
   const [error] = await withError(getMyUser());
-  if (isHttpError(error)) {
+  if (isHttpError(error) || isMalformedResponseError(error)) {
     logError(error, `Failed to connect to server ${url}`);
     process.exit(1);
   }
@@ -94,6 +102,11 @@ export const logError = (error: unknown, message: string) => {
   if (isHttpError(error)) {
     console.error(`${message}: ${error.status}`);
     console.error(JSON.stringify(error.data, undefined, 2));
+  } else if (isMalformedResponseError(error)) {
+    console.error(`${message}: ${error.message}`);
+    console.error(
+      'Check that the URL points at the Immich API, and that nothing in front of it (reverse proxy, SSO portal) is answering instead.',
+    );
   } else {
     console.error(`${message} - ${error}`);
   }
diff --git a/packages/sdk/src/fetch-errors.ts b/packages/sdk/src/fetch-errors.ts
index 306710fb8b..05fb427e6d 100644
--- a/packages/sdk/src/fetch-errors.ts
+++ b/packages/sdk/src/fetch-errors.ts
@@ -20,3 +20,24 @@ export interface ApiHttpError extends HttpError {
 export function isHttpError(error: unknown): error is ApiHttpError {
   return error instanceof HttpError;
 }
+
+export class MalformedResponseError extends Error {
+  override name = 'MalformedResponseError';
+
+  constructor(
+    reason: string,
+    readonly url: string,
+    readonly status: number,
+    readonly contentType: string | null,
+  ) {
+    super(
+      `${reason} (${url}, HTTP ${status}, content-type: ${contentType ?? 'none'})`,
+    );
+  }
+}
+
+export function isMalformedResponseError(
+  error: unknown,
+): error is MalformedResponseError {
+  return error instanceof MalformedResponseError;
+}
diff --git a/packages/sdk/src/index.ts b/packages/sdk/src/index.ts
index 7adbca4d7e..779376a4fd 100644
--- a/packages/sdk/src/index.ts
+++ b/packages/sdk/src/index.ts
@@ -1,4 +1,5 @@
 import { defaults } from './fetch-client.js';
+import { MalformedResponseError } from './fetch-errors.js';
 
 export * from './fetch-client.js';
 export * from './fetch-errors.js';
@@ -48,6 +49,37 @@ const assertNoApiKey = (headerKey: string) => {
   }
 };
 
+export const jsonOnly =
+  (impl?: typeof fetch): typeof fetch =>
+  async (input, options) => {
+    const response = await (impl ?? fetch)(input, options);
+
+    const expectsJson = new Headers(options?.headers)
+      .get('accept')
+      ?.includes('json');
+    if (!expectsJson || response.status === 204) {
+      return response;
+    }
+
+    const contentType = response.headers.get('content-type');
+    if (!contentType?.includes('json')) {
+      throw new MalformedResponseError(
+        'Expected a JSON response',
+        response.url,
+        response.status,
+        contentType,
+      );
+    }
+
+    return response;
+  };
+
+export const setFetch = (impl: typeof fetch) => {
+  defaults.fetch = jsonOnly(impl);
+};
+
+defaults.fetch = jsonOnly();
+
 export const getAssetOriginalPath = (id: string) => `/assets/${id}/original`;
 
 export const getAssetThumbnailPath = (id: string) => `/assets/${id}/thumbnail`;
diff --git a/web/src/lib/utils/server.ts b/web/src/lib/utils/server.ts
index e2d0048b20..1e8dc90673 100644
--- a/web/src/lib/utils/server.ts
+++ b/web/src/lib/utils/server.ts
@@ -1,4 +1,4 @@
-import { defaults } from '@immich/sdk';
+import { setFetch } from '@immich/sdk';
 import { memoize } from 'lodash-es';
 import { authManager } from '$lib/managers/auth-manager.svelte';
 import { featureFlagsManager } from '$lib/managers/feature-flags-manager.svelte';
@@ -11,7 +11,7 @@ async function _init(fetch: Fetch) {
   // set event.fetch on the fetch-client used by @immich/sdk
   // https://kit.svelte.dev/docs/load#making-fetch-requests
   // https://github.com/oazapfts/oazapfts/blob/main/README.md#fetch-options
-  defaults.fetch = fetch;
+  setFetch(fetch);
   await initLanguage();
   await serverConfigManager.init();
   await authManager.load();