diff --git a/README.md b/README.md
index b4ccf31f515..433d34047b8 100644
--- a/README.md
+++ b/README.md
@@ -250,9 +250,9 @@ Variable | Purpose
 -------- | -------
 ALLOWED_WEBHOOK_DOMAINS | comma-separated list of permitted domains to use in webhooks (e.g. webhook.site,zapier.com). You can set this to `*` to allow all domains, but if doing so, we recommend using a carefully locked-down proxy (see `GRIST_HTTPS_PROXY`) if you do not entirely trust users. Otherwise services on your internal network may become vulnerable to manipulation.
 APP_DOC_URL | doc worker url, set when starting an individual doc worker (other servers will find doc worker urls via redis)
-APP_DOC_INTERNAL_URL | like `APP_DOC_URL` but used by the home server to reach the server using an internal domain name resolution (like in a docker environment). Defaults to `APP_DOC_URL`
+APP_DOC_INTERNAL_URL | like `APP_DOC_URL` but used by the home server to reach the server using an internal domain name resolution (like in a docker environment). You may only define this value in the doc worker. Defaults to `APP_DOC_URL`
 APP_HOME_URL | url prefix for home api (home and doc servers need this)
-APP_HOME_INTERNAL_URL | like `APP_HOME_URL` but used by the home server to reach any home workers using an internal domain name resolution (like in a docker environment). Defaults to `APP_HOME_URL`
+APP_HOME_INTERNAL_URL | like `APP_HOME_URL` but used by the home server to reach any home workers using an internal domain name resolution (like in a docker environment). Also both home and doc workers need this. Defaults to `APP_HOME_URL`
 APP_STATIC_URL | url prefix for static resources
 APP_STATIC_INCLUDE_CUSTOM_CSS | set to "true" to include custom.css (from APP_STATIC_URL) in static pages
 APP_UNTRUSTED_URL   | URL at which to serve/expect plugin content.
diff --git a/app/common/gristUrls.ts b/app/common/gristUrls.ts
index 234f7ac0d2b..2659981974c 100644
--- a/app/common/gristUrls.ts
+++ b/app/common/gristUrls.ts
@@ -192,13 +192,12 @@ export function hostMatchesUrl(host?: string, url?: string) {
  *
  * @param {string?} host The host to check
  */
-export function isOwnInternalUrlHost(host?: string) {
-  if (process.env.APP_HOME_INTERNAL_URL) {
-    return hostMatchesUrl(host, process.env.APP_HOME_INTERNAL_URL);
-  } else if (process.env.APP_DOC_INTERNAL_URL) {
-    return hostMatchesUrl(host, process.env.APP_DOC_INTERNAL_URL);
+function isOwnInternalUrlHost(host?: string) {
+  // Note: APP_HOME_INTERNAL_URL may also defined in doc worker as well as in Home worker
+  if (process.env.APP_HOME_INTERNAL_URL && hostMatchesUrl(host, process.env.APP_HOME_INTERNAL_URL)) {
+    return true;
   }
-  return false;
+  return Boolean(process.env.APP_DOC_INTERNAL_URL) && hostMatchesUrl(host, process.env.APP_DOC_INTERNAL_URL);
 }
 
 /**
diff --git a/app/server/lib/Authorizer.ts b/app/server/lib/Authorizer.ts
index 761e76f2483..2ad7d134617 100644
--- a/app/server/lib/Authorizer.ts
+++ b/app/server/lib/Authorizer.ts
@@ -685,6 +685,9 @@ export function getTransitiveHeaders(req: Request): {[key: string]: string} {
   const XRequestedWith = req.get('X-Requested-With');
   const Origin = req.get('Origin');  // Pass along the original Origin since it may
                                      // play a role in granular access control.
+  const Host = req.get('Host');      // Also pass along the original Host, as we need it since
+                                     // the destination compares that with the Origin header.
+
   const result: Record<string, string> = {
     ...(Authorization ? { Authorization } : undefined),
     ...(Cookie ? { Cookie } : undefined),
@@ -692,6 +695,7 @@ export function getTransitiveHeaders(req: Request): {[key: string]: string} {
     ...(PermitHeader ? { Permit: PermitHeader } : undefined),
     ...(XRequestedWith ? { 'X-Requested-With': XRequestedWith } : undefined),
     ...(Origin ? { Origin } : undefined),
+    ...(Host ? { Host } : undefined),
   };
   const extraHeader = process.env.GRIST_FORWARD_AUTH_HEADER;
   const extraHeaderValue = extraHeader && req.get(extraHeader);
diff --git a/app/server/lib/requestUtils.ts b/app/server/lib/requestUtils.ts
index 11617fef59b..e04e737635b 100644
--- a/app/server/lib/requestUtils.ts
+++ b/app/server/lib/requestUtils.ts
@@ -1,7 +1,5 @@
 import {ApiError} from 'app/common/ApiError';
-import {
-  DEFAULT_HOME_SUBDOMAIN, isOrgInPathOnly, isOwnInternalUrlHost, parseSubdomain, sanitizePathTail
-} from 'app/common/gristUrls';
+import { DEFAULT_HOME_SUBDOMAIN, isOrgInPathOnly, parseSubdomain, sanitizePathTail } from 'app/common/gristUrls';
 import * as gutil from 'app/common/gutil';
 import {DocScope, QueryResult, Scope} from 'app/gen-server/lib/HomeDBManager';
 import {getUser, getUserId, RequestWithLogin} from 'app/server/lib/Authorizer';
@@ -89,8 +87,6 @@ export function trustOrigin(req: Request, resp: Response): boolean {
   if (!origin) { return true; } // Not a CORS request.
   if (process.env.GRIST_HOST && req.hostname === process.env.GRIST_HOST) { return true; }
 
-  if (isOwnInternalUrlHost(req.get('Host'))) { return true; }
-
   if (!allowHost(req, new URL(origin))) { return false; }
 
   // For a request to a custom domain, the full hostname must match.