diff --git a/README.md b/README.md
index 5c045b78..c15445e6 100644
--- a/README.md
+++ b/README.md
@@ -213,9 +213,9 @@ variables (e.g. `URL_BASE_TRUSTED=https://mailtrain.domain.com (and more env-var
 | PORT_TRUSTED     | sets the trusted port of the instance (default: 3000)                 |
 | PORT_SANDBOX     | sets the sandbox port of the instance (default: 3003)                 |
 | PORT_PUBLIC      | sets the public port of the instance (default: 3004)                  |
-| URL_BASE_TRUSTED | sets the trusted url of the instance (default: http://localhost)      |
-| URL_BASE_SANDBOX | sets the sandbox url of the instance (default: http://localhost)      |
-| URL_BASE_PUBLIC  | sets the public url of the instance (default: http://localhost)       |
+| URL_BASE_TRUSTED | sets the trusted url of the instance (default: http://localhost:3000) |
+| URL_BASE_SANDBOX | sets the sandbox url of the instance (default: http://localhost:3003) |
+| URL_BASE_PUBLIC  | sets the public url of the instance (default: http://localhost:3004)  |
 | WWW_HOST         | sets the address that the server binds to (default: 0.0.0.0)          |
 | WWW_PROXY        | use if Mailtrain is behind an http reverse proxy (default: false)     |
 | WWW_SECRET       | sets the secret for the express session (default: `$(pwgen -1)`)      |
diff --git a/docker-entrypoint.sh b/docker-entrypoint.sh
index b088ab88..f2e879f9 100644
--- a/docker-entrypoint.sh
+++ b/docker-entrypoint.sh
@@ -5,12 +5,12 @@ set -e
 
 default_filter="(|(username={{username}})(mail={{username}}))"
 
-URL_BASE_TRUSTED=${URL_BASE_TRUSTED:-'http://localhost'}
-URL_BASE_SANDBOX=${URL_BASE_SANDBOX:-'http://localhost'}
-URL_BASE_PUBLIC=${URL_BASE_PUBLIC:-'http://localhost'}
 PORT_TRUSTED=${PORT_TRUSTED:-'3000'}
 PORT_SANDBOX=${PORT_SANDBOX:-'3003'}
 PORT_PUBLIC=${PORT_PUBLIC:-'3004'}
+URL_BASE_TRUSTED=${URL_BASE_TRUSTED:-"http://localhost:${PORT_TRUSTED}"}
+URL_BASE_SANDBOX=${URL_BASE_SANDBOX:-"http://localhost:${PORT_SANDBOX}"}
+URL_BASE_PUBLIC=${URL_BASE_PUBLIC:-"http://localhost:${PORT_PUBLIC}"}
 WWW_HOST=${WWW_HOST:-'0.0.0.0'}
 WWW_PROXY=${WWW_PROXY:-'false'}
 WWW_SECRET=${WWW_SECRET:-$(pwgen -1)}
@@ -58,9 +58,9 @@ www:
   trustedPort: $PORT_TRUSTED
   sandboxPort: $PORT_SANDBOX
   publicPort: $PORT_PUBLIC
-  trustedUrlBase: $URL_BASE_TRUSTED:${PORT_TRUSTED}
-  sandboxUrlBase: $URL_BASE_SANDBOX:${PORT_SANDBOX}
-  publicUrlBase: $URL_BASE_PUBLIC:${PORT_PUBLIC}
+  trustedUrlBase: $URL_BASE_TRUSTED
+  sandboxUrlBase: $URL_BASE_SANDBOX
+  publicUrlBase: $URL_BASE_PUBLIC
 
 mysql:
   host: $MYSQL_HOST