diff --git a/libraries/src/Form/Rule/FilePathRule.php b/libraries/src/Form/Rule/FilePathRule.php
index 964e68d5b0965..a752c95cf5ae0 100644
--- a/libraries/src/Form/Rule/FilePathRule.php
+++ b/libraries/src/Form/Rule/FilePathRule.php
@@ -50,7 +50,7 @@ public function test(\SimpleXMLElement $element, $value, $group = null, Registry
 		}
 
 		// Append the root path
-		$value = JPATH_ROOT . '/' . $value;
+		$value = JPATH_ROOT . DIRECTORY_SEPARATOR . $value;
 
 		try
 		{