diff --git a/lib/Less/Functions.php b/lib/Less/Functions.php
index 6dfa7626..56e62e28 100644
--- a/lib/Less/Functions.php
+++ b/lib/Less/Functions.php
@@ -67,9 +67,21 @@ public static function scaled( $n, $size = 255 ) {
 	}
 
 	public function rgb( $r = null, $g = null, $b = null ) {
-		if ( $r === null || $g === null || $b === null ) {
-			throw new Less_Exception_Compiler( "rgb expects three parameters" );
+		$components = func_get_args();
+
+		if (count( $components ) != 3)
+		{
+			return null;
+		}
+
+		foreach ( $components AS $component )
+		{
+			if ( !$component instanceof Less_Tree_Dimension )
+			{
+				return null;
+			}
 		}
+
 		return $this->rgba( $r, $g, $b, 1.0 );
 	}
 
@@ -81,28 +93,23 @@ public function rgba( $r = null, $g = null, $b = null, $a = null ) {
 		return new Less_Tree_Color( $rgb, $a );
 	}
 
-	public function hsl( $h, $s, $l ) {
-		if (self::isLessHsl( $h, $s, $l )) {
-			return $this->hsla( $h, $s, $l, 1.0 );
-		}
-
-		return 'hsl(' . $h . ')';
-	}
+	public function hsl( $h, $s = null, $l = null ) {
+		$components = func_get_args();
 
-	protected function isLessHsl( $h, $s, $l ) {
-		$hsl = func_get_args();
-
-		if (count( $hsl ) != 3) {
-			return false;
+		if (count( $components ) != 3)
+		{
+			return null;
 		}
 
-		foreach ( $hsl AS $arg ) {
-			if ( !$arg instanceof Less_Tree_Dimension ) {
-				return false;
+		foreach ( $components AS $component )
+		{
+			if ( !$component instanceof Less_Tree_Dimension )
+			{
+				return null;
 			}
 		}
 
-		return true;
+		return $this->hsla( $h, $s, $l, 1.0 );
 	}
 
 	public function hsla( $h, $s, $l, $a ) {