diff --git a/docker/www/Dockerfile b/docker/www/Dockerfile
index 66d2d2523..d6490cf8a 100644
--- a/docker/www/Dockerfile
+++ b/docker/www/Dockerfile
@@ -1,4 +1,4 @@
-FROM php:7.1-apache
+FROM php:7.3-apache-stretch
 
 ARG XDEBUG_REMOTE_ENABLE=1
 ARG XDEBUG_REMOTE_CONNECT_BACK=0
diff --git a/forum/qa-include/app/format.php b/forum/qa-include/app/format.php
index b5a370255..03a6c3c93 100644
--- a/forum/qa-include/app/format.php
+++ b/forum/qa-include/app/format.php
@@ -334,7 +334,7 @@ function qa_post_html_fields($post, $userid, $cookieid, $usershtml, $dummy, $opt
 			if (@$options['categoryview'] && isset($post['categoryname']) && isset($post['categorybackpath'])) {
 				$favoriteclass='';
 
-				if (count(@$favoritemap['category'])) {
+				if (isset($favoritemap['category']) && count(@$favoritemap['category'])) {
 					if (@$favoritemap['category'][$post['categorybackpath']])
 						$favoriteclass=' qa-cat-favorited';
 
@@ -1507,7 +1507,7 @@ function qa_set_display_rules(&$qa_content, $effects)
 	also combine multiple DOM IDs using JavaScript(=PHP) operators. This is twisted but rather convenient.
 */
 	{
-		$function='qa_display_rule_'.count(@$qa_content['script_lines']);
+		$function='qa_display_rule_'.count($qa_content['script_lines'] ?? []);
 
 		$keysourceids=array();
 
diff --git a/forum/qa-include/app/q-list.php b/forum/qa-include/app/q-list.php
index b844b69f3..9c71cc9f1 100644
--- a/forum/qa-include/app/q-list.php
+++ b/forum/qa-include/app/q-list.php
@@ -110,7 +110,7 @@ function qa_q_list_page_content($questions, $pagesize, $start, $count, $sometitl
 		if (empty($qa_content['page_links']))
 			$qa_content['suggest_next']=$suggest;
 
-		if (qa_using_categories() && count($navcategories) && isset($categorypathprefix))
+		if (isset($navcategories, $categorypathprefix) && qa_using_categories() && count($navcategories))
 			$qa_content['navigation']['cat']=qa_category_navigation($navcategories, $categoryid, $categorypathprefix, $categoryqcount, $categoryparams);
 
 		if (isset($feedpathprefix) && (qa_opt('feed_per_category') || !isset($categoryid)) )
diff --git a/forum/qa-include/qa-page.php b/forum/qa-include/qa-page.php
index 4c127747b..ca6257642 100644
--- a/forum/qa-include/qa-page.php
+++ b/forum/qa-include/qa-page.php
@@ -517,11 +517,12 @@ function qa_content_prepare($voting=false, $categoryids=null)
 		$navpages=qa_db_get_pending_result('navpages');
 		$widgets=qa_db_get_pending_result('widgets');
 
-		if (isset($categoryids) && !is_array($categoryids)) // accept old-style parameter
-			$categoryids=array($categoryids);
-
-		$lastcategoryid=count($categoryids) ? end($categoryids) : null;
-		$charset = 'utf-8';
+        // accept old-style parameter
+		if (isset($categoryids) && !is_array($categoryids)) {
+            $categoryids = [$categoryids];
+            $lastcategoryid = count($categoryids) ? end($categoryids) : null;
+        }
+        $charset = 'utf-8';
 
 		$qa_content=array(
 			'content_type' => 'text/html; charset='.$charset,
diff --git a/forum/qa-include/qa-theme-base.php b/forum/qa-include/qa-theme-base.php
index b48fca095..726c6ed7c 100644
--- a/forum/qa-include/qa-theme-base.php
+++ b/forum/qa-include/qa-theme-base.php
@@ -174,7 +174,7 @@ public function widgets($region, $place)
 	Output the widgets (as provided in $this->content['widgets']) for $region and $place
 */
 	{
-		if (count(@$this->content['widgets'][$region][$place])) {
+		if (isset($this->content['widgets'][$region][$place]) && count(@$this->content['widgets'][$region][$place])) {
 			$this->output('<div class="qa-widgets-'.$region.' qa-widgets-'.$region.'-'.$place.'">');
 
 			foreach ($this->content['widgets'][$region][$place] as $module) {
@@ -574,7 +574,7 @@ public function nav_item($key, $navlink, $class, $level=null)
 			(@$navlink['state'] ? (' qa-'.$class.'-'.$navlink['state']) : '').' qa-'.$class.'-'.$suffix.'">');
 		$this->nav_link($navlink, $class);
 
-		if (count(@$navlink['subnav']))
+		if (isset($navlink['subnav']) && count(@$navlink['subnav']))
 			$this->nav_list($navlink['subnav'], $class, 1+$level);
 
 		$this->output('</li>');
diff --git a/forum/qa-include/vendor/PHPMailer/PHPMailerAutoload.php b/forum/qa-include/vendor/PHPMailer/PHPMailerAutoload.php
index ac47f4520..5ab42df12 100644
--- a/forum/qa-include/vendor/PHPMailer/PHPMailerAutoload.php
+++ b/forum/qa-include/vendor/PHPMailer/PHPMailerAutoload.php
@@ -30,20 +30,4 @@ function PHPMailerAutoload($classname)
     }
 }
 
-if (version_compare(PHP_VERSION, '5.1.2', '>=')) {
-    //SPL autoloading was introduced in PHP 5.1.2
-    if (version_compare(PHP_VERSION, '5.3.0', '>=')) {
-        spl_autoload_register('PHPMailerAutoload', true, true);
-    } else {
-        spl_autoload_register('PHPMailerAutoload');
-    }
-} else {
-    /**
-     * Fall back to traditional autoload for old PHP versions
-     * @param string $classname The name of the class to load
-     */
-    function __autoload($classname)
-    {
-        PHPMailerAutoload($classname);
-    }
-}
+spl_autoload_register('PHPMailerAutoload', true, true);
diff --git a/forum/qa-plugin/q2apro-on-site-notifications/q2apro-onsitenotifications-page.php b/forum/qa-plugin/q2apro-on-site-notifications/q2apro-onsitenotifications-page.php
index 76be6fd05..3d99acb8e 100644
--- a/forum/qa-plugin/q2apro-on-site-notifications/q2apro-onsitenotifications-page.php
+++ b/forum/qa-plugin/q2apro-on-site-notifications/q2apro-onsitenotifications-page.php
@@ -226,7 +226,7 @@ public function process_request($request)
                         $itemIcon = '<div class="nicon nbestanswer"></div>';
                         break;
                     default:
-                        continue;
+                        continue 2;
                 }
             }