Phpmyadmin host not found

I tried to add phpmyadmin to the docker-compose.yml, but it complaints that it cannot find the host mysql.
What do I miss?


version: ‘2’

services:
nginx:
image: nginx:latest
ports:
- '80:80’
volumes:
- ./nginx:/etc/nginx/conf.d
- ./logs/nginx:/var/log/nginx
- ./wordpress:/var/www/html
links:
- wordpress
restart: always

mysql:
image: mariadb
ports:
- '3306:3306’
volumes:
- ./db-data:/var/lib/mysql
environment:
- MYSQL_ROOT_PASSWORD=aqwe123
restart: always

wordpress:
image: wordpress:4.7.1-php7.0-fpm
ports:
- '9000:9000’
volumes:
- ./wordpress:/var/www/html
environment:
- WORDPRESS_DB_NAME=wpdb
- WORDPRESS_TABLE_PREFIX=wp_
- WORDPRESS_DB_HOST=mysql
- WORDPRESS_DB_PASSWORD=aqwe123
links:
- mysql
restart: always

phpmyadmin:
depends_on:
- mysql
image: phpmyadmin/phpmyadmin
restart: always
ports:
- 8081:80
environment:
PMA_HOST: mysql
MYSQL_ROOT_PASSWORD: aqwe123
networks:
- back

networks:
back:

volumes:
db_data: