diff --git a/category.php b/category.php
index f91ad942c..f0a5161f7 100644
--- a/category.php
+++ b/category.php
@@ -39,6 +39,9 @@ if ( isset($_GET['cat']) )
   {
     $url_params['section'] = 'categories';
     $url_params['category'] = $_GET['cat'];
+    $result = get_cat_info($url_params['category']);
+    if ( !empty($result) )
+      $url_params['cat_name'] = $result['name'];
   }
   elseif ( in_array($_GET['cat'],
               array('best_rated','most_visited','recent_pics','recent_cats')
@@ -47,6 +50,10 @@ if ( isset($_GET['cat']) )
   {
     $url_params['section'] = $_GET['cat'];
   }
+  else
+  {
+    page_not_found('');
+  }
 }
 
 redirect ( make_index_url($url_params) );
diff --git a/include/functions_category.inc.php b/include/functions_category.inc.php
index a671474ef..2aff86975 100644
--- a/include/functions_category.inc.php
+++ b/include/functions_category.inc.php
@@ -118,6 +118,8 @@ SELECT '.implode(',', $infos).'
   WHERE id = '.$id.'
 ;';
   $row = mysql_fetch_array(pwg_query($query));
+  if (empty($row))
+    return null;
 
   $cat = array();
   foreach ($infos as $info)
diff --git a/include/functions_html.inc.php b/include/functions_html.inc.php
index bc967b752..65cbc879c 100644
--- a/include/functions_html.inc.php
+++ b/include/functions_html.inc.php
@@ -591,4 +591,22 @@ function access_denied()
     redirect($login_url);
   }
 }
+
+/**
+ * exits the current script with 404 code when a page cannot be found
+ * @param string msg a message to display
+ * @param string alternate_url redirect to this url
+ */
+function page_not_found($msg, $alternate_url=null)
+{
+  header('HTTP/1.1 404 Not found');
+  header('Status: 404 Not found');
+  if ($alternate_url==null)
+    $alternate_url = make_index_url();
+  redirect( $alternate_url,
+    '<div style="text-align:left; margin-left:5em;margin-bottom:5em;">
+<h1 style="text-align:left; font-size:36px;">Page not found</h1><br/>'
+.$msg.'</div>',
+    5 );
+}
 ?>
diff --git a/include/section_init.inc.php b/include/section_init.inc.php
index 3a27882ba..1d5949e63 100644
--- a/include/section_init.inc.php
+++ b/include/section_init.inc.php
@@ -197,7 +197,7 @@ SELECT name, url_name, id
   }
   if ( empty($page['tags']) )
   {
-    die('Fatal: no existing tag');
+    page_not_found('Requested tag does not exist', get_root_url().'tags.php' );
   }
 }
 else if (0 === strpos($tokens[$next_token], 'fav'))
@@ -316,6 +316,10 @@ if ('categories' == $page['section'])
   if (isset($page['category']))
   {
     $result = get_cat_info($page['category']);
+    if (empty($result))
+    {
+      page_not_found('Requested category does not exist' );
+    }
 
     $page = array_merge(
       $page,
diff --git a/picture.php b/picture.php
index 486e303cb..ed143723f 100644
--- a/picture.php
+++ b/picture.php
@@ -42,7 +42,8 @@ if (isset($page['category']))
 // displayed, and execution is stopped
 if (!in_array($page['image_id'], $page['items']))
 {
-  die('Fatal: this picture does not belong to this section');
+  page_not_found('The requested image does not belong to this image set',
+      duplicate_index_url() );
 }
 
 // +-----------------------------------------------------------------------+