diff --git a/phpBB/includes/db/dbal.php b/phpBB/includes/db/dbal.php
index df6e453329..ffe5228665 100644
--- a/phpBB/includes/db/dbal.php
+++ b/phpBB/includes/db/dbal.php
@@ -300,22 +300,35 @@ class dbal
 	}
 
 	/**
-	* Build IN, NOT IN, = and <> sql comparison string.
+	* Build IN or NOT IN sql comparison string, uses <> or = on single element
+	* arrays to improve comparison speed
 	* @access public
+	* @param	string	$field				name of the sql column that shall be compared
+	* @param	array	$array				array of values that are allowed (IN) or not allowed (NOT IN)
+	* @param	bool	$negate				true for IN (), false for NOT IN ()
+	* @param	bool	$allow_empty_set	Allow $array to be empty, this function will return 1=1 or 1=0 then
 	*/
-	function sql_in_set($field, $array, $negate = false)
+	function sql_in_set($field, $array, $negate = false, $allow_empty_set = false)
 	{
 		if (!sizeof($array))
 		{
-			// NOT IN () actually means everything so use a tautology
-			if ($negate)
+			if (!$allow_empty_set)
 			{
-				return '1=1';
+				// Print the backtrace to help identifying the location of the problematic code
+				$this->sql_error('No values specified for SQL IN comparison');
 			}
-			// IN () actually means nothing so use a contradiction
 			else
 			{
-				return '1=0';
+				// NOT IN () actually means everything so use a tautology
+				if ($negate)
+				{
+					return '1=1';
+				}
+				// IN () actually means nothing so use a contradiction
+				else
+				{
+					return '1=0';
+				}
 			}
 		}