diff --git a/workflow/engine/classes/class.system.php b/workflow/engine/classes/class.system.php
index 4f2e73190..e450bcf00 100755
--- a/workflow/engine/classes/class.system.php
+++ b/workflow/engine/classes/class.system.php
@@ -706,7 +706,10 @@ class System {
   * @return $sContent
   */
   public static function getPluginSchema($pluginName) {
-    return System::getSchema(PATH_PLUGINS . $pluginName . "/config/schema.xml");
+    if (file_exists(PATH_PLUGINS . $pluginName . "/config/schema.xml"))
+      return System::getSchema(PATH_PLUGINS . $pluginName . "/config/schema.xml");
+    else
+      return false;
   }
 
   /**
diff --git a/workflow/engine/classes/class.wsTools.php b/workflow/engine/classes/class.wsTools.php
index e548c8fec..4f44d3479 100644
--- a/workflow/engine/classes/class.wsTools.php
+++ b/workflow/engine/classes/class.wsTools.php
@@ -304,7 +304,8 @@ class workspaceTools {
   public function upgradePluginsDatabase() {
     foreach (System::getPlugins() as $pluginName) {
       $pluginSchema = System::getPluginSchema($pluginName);
-      $this->upgradeSchema($pluginSchema);
+      if ($pluginSchema !== false)
+        $this->upgradeSchema($pluginSchema);
     }
   }
 
@@ -320,9 +321,8 @@ class workspaceTools {
       throw new Exception("Only MySQL is supported");
     }
 
-    $currentSchema = System::getSchema();
     $workspaceSchema = $this->getSchema();
-    $changes = System::compareSchema($workspaceSchema, $currentSchema);
+    $changes = System::compareSchema($workspaceSchema, $schema);
     $changed = (count($changes['tablesToAdd']) > 0 ||
                 count($changes['tablesToAlter']) > 0 ||
                 count($changes['tablesWithNewIndex']) > 0 ||