diff --git a/manifests/instance.pp b/manifests/instance.pp
index 6003031..3226382 100644
--- a/manifests/instance.pp
+++ b/manifests/instance.pp
@@ -1,157 +1,165 @@
 # == Defined Type: gunicorn::instance
 #
 # gunicorn::instance defines an instance of gunicorn
 #
 # === Parameters
 #
 # [*ensure*]
 #   Whether the instance should be enabled, present (but disabled) or absent.
 #
+# [*environment*]
+#   A hash of environment variables to start the service with.
+#
 # [*executable*]
 #   The wsgi callable to pass to gunicorn
 #
 # [*settings*]
 #   a hash of settings for the given site.
 #
 # === Examples
 #
 #  gunicorn::instance {'foo':
 #    ensure      => enabled,
+#    environment => {
+#      FOOENV => 'foovar',
+#    }
 #    executable  => 'foo.wsgi:app'
 #    user        => 'foouser',
 #    group       => 'foogroup',
 #    config_mode => 0644
 #    settings    => {
 #      plugin              => 'python3',
 #      protocol            => $uwsgi_protocol,
 #      socket              => $uwsgi_listen_address,
 #      workers             => $uwsgi_workers,
 #      max_requests        => $uwsgi_max_requests,
 #      max_requests_delta  => $uwsgi_max_requests_delta,
 #      worker_reload_mercy => $uwsgi_reload_mercy,
 #      reload_mercy        => $uwsgi_reload_mercy,
 #      uid                 => $user,
 #      gid                 => $user,
 #      module              => 'swh.storage.api.server',
 #      callable            => 'run_from_webserver',
 #    }
 #  }
 #
 # === Authors
 #
 # Nicolas Dandrimont <nicolas@dandrimont.eu>
 #
 # === Copyright
 #
 # Copyright 2017 The Software Heritage developers
 #
 define gunicorn::instance (
   $executable,
   $user = 'root',
   $group = 'root',
   $ensure = 'enabled',
   $config_mode = '0644',
   $working_dir = undef,
   $log_only_errors = true,
-  $settings = {}
+  $settings = {},
+  $environment = {}
 ) {
   $config_file = "/etc/gunicorn/instances/${name}.cfg"
   $service_name = "gunicorn-${name}"
   $service_file = "/etc/systemd/system/${service_name}.service"
   $tmpfiles_file = "/etc/tmpfiles.d/${service_name}.conf"
   $runtime_dir = "/run/gunicorn/${name}"
 
   if $working_dir {
     $working_dir_override = $working_dir
   } else {
     $working_dir_override = $runtime_dir
   }
 
   if $log_only_errors {
     $log_only_errors_str = 'True'
   } else {
     $log_only_errors_str = 'False'
   }
 
   case $ensure {
     default: { err("Unknown value ensure => ${ensure}.") }
     'enabled', 'present': {
 
       include ::gunicorn
 
       # Uses variables:
       #  - $settings
       #  - $name
       #  - $log_only_errors_str
       file {$config_file:
         ensure  => present,
         owner   => $user,
         group   => $group,
         mode    => $config_mode,
         content => template('gunicorn/gunicorn-instance.cfg.erb'),
         notify  => Service[$service_name],
       }
 
       # Uses variables:
       #  - $config_file
+      #  - $environment
       #  - $executable
       #  - $group
       #  - $name
       #  - $runtime_dir
       #  - $user
       #  - $working_dir_override
       file {$service_file:
         ensure  => present,
         owner   => 'root',
         group   => 'root',
         mode    => '0644',
         content => template('gunicorn/gunicorn-instance.service.erb'),
         notify  => Exec['systemd-daemon-reload'],
       }
 
       # Uses variables:
       #  - $group
       #  - $name
       #  - $runtime_dir
       #  - $user
       file {$tmpfiles_file:
         ensure  => present,
         owner   => 'root',
         group   => 'root',
         mode    => '0644',
         content => template('gunicorn/gunicorn-instance.tmpfiles.erb'),
         notify  => Exec["systemd-tmpfiles-update-${service_name}"],
       }
 
       exec {"systemd-tmpfiles-update-${service_name}":
         path        => '/sbin:/usr/sbin:/bin:/usr/bin',
         command     => "systemd-tmpfiles --create ${tmpfiles_file}",
         refreshonly => true,
         require     => File[$tmpfiles_file]
       }
 
       $service_enable = $ensure ? {
         'enabled' => true,
         'present' => undef,
       }
 
       service {$service_name:
         ensure  => 'running',
         enable  => $service_enable,
         restart => "/bin/systemctl reload ${service_name}.service",
         require => [
           File[$service_file],
           File[$config_file],
           Exec['systemd-daemon-reload'],
         ],
       }
     }
 
     'absent': {
       file {[$tmpfiles_file, $service_file]:
         ensure => 'absent'
       }
     }
   }
 }
 
diff --git a/templates/gunicorn-instance.service.erb b/templates/gunicorn-instance.service.erb
index d37fd7f..73a32af 100644
--- a/templates/gunicorn-instance.service.erb
+++ b/templates/gunicorn-instance.service.erb
@@ -1,21 +1,24 @@
 # File managed by puppet (class gunicorn::instance <%= @name %>), changes will be lost
 
 [Unit]
 Description=Gunicorn instance <%= @name %>
 ConditionPathExists=/etc/gunicorn/instances/<%= @name %>.cfg
 PartOf=gunicorn.service
 ReloadPropagatedFrom=gunicorn.service
 Before=gunicorn.service
 
 [Service]
 User=<%= @user %>
 Group=<%= @group %>
 PIDFile=<%= @runtime_dir %>/pidfile
 RuntimeDirectory=<%= @runtime_dir %>
 WorkingDirectory=<%= @working_dir_override %>
+<% @environment.each do |key, value| %>
+Environment=<%= key %>=<%= value %>
+<% end %>
 ExecStart=/usr/bin/gunicorn3 -p <%= @runtime_dir %>/pidfile -c <%= @config_file %> <%= @executable %>
 ExecStop=/bin/kill -TERM $MAINPID
 ExecReload=/bin/kill -HUP $MAINPID
 
 [Install]
 WantedBy=multi-user.target