diff --git a/contribution/style/demo/manager.php b/contribution/style/demo/manager.php
index e25259be9..2933ee645 100644
--- a/contribution/style/demo/manager.php
+++ b/contribution/style/demo/manager.php
@@ -32,6 +32,9 @@ class manager
 	/** @var \phpbb\db\db_interface */
 	protected $db;
 
+	/** @var string */
+	protected $table_prefix;
+
 	/** @var int */
 	protected $branch;
 
@@ -151,9 +154,18 @@ protected function perform_action($action)
 
 		$hook_url = $this->ext_config->demo_style_hook[$this->branch];
 		$context = stream_context_create($options);
-		$result = file_get_contents($hook_url, false, $context, 0, 50);
+		// A failing hook must degrade to an error result; the warning would
+		// otherwise be turned into an exception and lose the JSON reply.
+		$result = @file_get_contents($hook_url, false, $context, 0, 50);
 		$this->delete_auth_key($key);
 
+		if ($result === false)
+		{
+			return array(
+				'id'	=> 0,
+				'error'	=> $this->user->lang('UNKNOWN_ERROR'),
+			);
+		}
 		return $this->get_result($result);
 	}
 
diff --git a/contribution/style/type.php b/contribution/style/type.php
index c151f2f29..ff9385281 100644
--- a/contribution/style/type.php
+++ b/contribution/style/type.php
@@ -208,17 +208,25 @@ public function install_demo(\titania_contribution $contrib, \titania_revision $
 
 		$demo_url = '';
 
-		if ($this->demo_manager->configure($branch, $contrib, $package))
+		// A demo failure must not abort the approval or the AJAX reply.
+		try
 		{
-			$result = $this->demo_manager->install();
-
-			if (empty($result['error']))
+			if ($this->demo_manager->configure($branch, $contrib, $package))
 			{
-				$demo_url = $this->demo_manager->get_demo_url($branch, $result['id']);
-				$contrib->set_demo_url($branch, $demo_url);
-				$contrib->submit();
+				$result = $this->demo_manager->install();
+
+				if (empty($result['error']))
+				{
+					$demo_url = $this->demo_manager->get_demo_url($branch, $result['id']);
+					$contrib->set_demo_url($branch, $demo_url);
+					$contrib->submit();
+				}
 			}
 		}
+		catch (\Throwable $e)
+		{
+			$demo_url = '';
+		}
 		$package->cleanup();
 
 		return $demo_url;
diff --git a/controller/contribution/manage.php b/controller/contribution/manage.php
index a4ba5f753..3ba079cf3 100644
--- a/controller/contribution/manage.php
+++ b/controller/contribution/manage.php
@@ -629,6 +629,14 @@ protected function install_demo($branch)
 			$revision->__set_array($this->contrib->download[$branch]);
 			$demo_url = $this->contrib->type->install_demo($this->contrib, $revision);
 		}
+
+		if ($demo_url === '')
+		{
+			return array(
+				'MESSAGE_TITLE'	=> $this->user->lang('INFORMATION'),
+				'MESSAGE_TEXT'	=> $this->user->lang('DEMO_INSTALL_FAILED'),
+			);
+		}
 		return array(
 			'url'	=> $demo_url,
 		);
diff --git a/language/en/contributions.php b/language/en/contributions.php
index b704695d3..35c9bdca8 100644
--- a/language/en/contributions.php
+++ b/language/en/contributions.php
@@ -101,6 +101,7 @@
 	'DELETE_CONTRIBUTION_EXPLAIN'			=> 'Permanently remove this contribution (use the contribution status field if you need to hide it).',
 	'DELETE_REVISION'						=> 'Delete Revision',
 	'DELETE_REVISION_EXPLAIN'				=> 'Permanently remove this revision (use the revision status field if you need to hide it).',
+	'DEMO_INSTALL_FAILED'					=> 'The style could not be installed on the demo board.',
 	'DEMO_URL'								=> 'Demo URL',
 	'DEMO_URL_EXPLAIN'						=> 'Location of the demonstration',
 	'DEPENDENCIES'							=> 'Dependencies',
diff --git a/misc/style_demo_hooks/phpBB_3.3.x/style_demo_install.php b/misc/style_demo_hooks/phpBB_3.3.x/style_demo_install.php
index 46a0f2030..683941d8c 100644
--- a/misc/style_demo_hooks/phpBB_3.3.x/style_demo_install.php
+++ b/misc/style_demo_hooks/phpBB_3.3.x/style_demo_install.php
@@ -20,6 +20,12 @@
 include($phpbb_root_path . 'includes/style_demo_manager.' . $phpEx);
 include($phpbb_root_path . 'includes/style_demo_hook.' . $phpEx);
 
+// acp_styles logs the installation and reads the user's id and ip from the
+// session, so one has to exist before the manager runs.
+$user->session_begin();
+$auth->acl($user->data);
+$user->setup();
+
 $hook = new \titania_style_demo_hook($config, $db, $user, $phpbb_root_path, $phpEx);
 $result = $hook->run($request->variable('key', ''));
 
diff --git a/misc/style_demo_hooks/style_demo_hook.php b/misc/style_demo_hooks/style_demo_hook.php
index cae954255..2420986c5 100644
--- a/misc/style_demo_hooks/style_demo_hook.php
+++ b/misc/style_demo_hooks/style_demo_hook.php
@@ -25,6 +25,9 @@ class titania_style_demo_hook
 	/** @var string */
 	protected $php_ext;
 
+	/** @var titania_demo_manager */
+	protected $manager;
+
 	/**
 	* Constructor.
 	*