diff --git a/htdocs/index.php b/htdocs/index.php
index 393f0d21..2af19b7b 100644
--- a/htdocs/index.php
+++ b/htdocs/index.php
@@ -136,36 +136,46 @@ else if ($n && $p[0] == SALT_USER)
       {
 	$tmp = explode("-", $p[2]);
 	$id = intval($tmp[0]);
-	$THEME = new Theme($id);
-	unset($tmp, $id);
-	$template->assign("cur_theme", $THEME);
 
-	if ($n == 4 || ($n >= 5 && $p[4] == "submission"))
-	  $id_exo = $p[3];
-	else if ($n == 3)
-	{
-	  foreach($THEME->get_exercices_ordered() as $exo)
-	  {
-	    if (! $exo->has_solved($TEAM))
-	      break;
-	  }
-	  $id_exo = $exo->id;
-	}
+        if ($id == 0)
+            $page = "404";
+        else
+        {
+          try
+          {
+            $THEME = new Theme($id);
+            unset($tmp, $id);
+            $template->assign("cur_theme", $THEME);
 
-	try
-	{
-	  $EXERCICE = new Exercice($id_exo, $THEME);
-	  $template->assign("cur_exercice", $EXERCICE);
-	  $page = require("team/exercice.php");
-	}
-	catch(ExerciceNotFoundException $e)
-	{
-	  $page = "404";
-	}
-	catch(InvalidThemeException $e)
-	{
-	  $page = "404";
-	}
+            if ($n == 4 || ($n >= 5 && $p[4] == "submission"))
+              $id_exo = $p[3];
+            else if ($n == 3)
+            {
+              foreach($THEME->get_exercices_ordered() as $exo)
+              {
+                if (! $exo->has_solved($TEAM))
+                  break;
+              }
+              $id_exo = $exo->id;
+            }
+
+            $EXERCICE = new Exercice($id_exo, $THEME);
+            $template->assign("cur_exercice", $EXERCICE);
+            $page = require("team/exercice.php");
+          }
+          catch(ExerciceNotFoundException $e)
+          {
+            $page = "404";
+          }
+          catch(InvalidThemeException $e)
+          {
+            $page = "404";
+          }
+          catch(ThemeNotFoundException $e)
+          {
+            $page = "404";
+          }
+        }
       }
     }
   }
diff --git a/onyx/include/common/Theme.class.php b/onyx/include/common/Theme.class.php
index 1c470bc1..15f81d41 100644
--- a/onyx/include/common/Theme.class.php
+++ b/onyx/include/common/Theme.class.php
@@ -20,6 +20,11 @@ class Theme
 	$this->id = $res['id'];
 	$this->name = $res['name'];
       }
+      else
+      {
+        $db->deconnexion();
+	throw new ThemeNotFoundException();
+      }
       $db->deconnexion();
     }
   }
@@ -137,3 +142,8 @@ class Theme
     return $array;
   }
 }
+
+class ThemeNotFoundException extends Exception
+{
+}
+