diff --git a/system/codeigniter/Compat.php b/system/codeigniter/Compat.php
index 3c5f70d..108b0a1 100644
--- a/system/codeigniter/Compat.php
+++ b/system/codeigniter/Compat.php
@@ -55,6 +55,11 @@
 {
 	function ctype_digit($str)
 	{
+		if (! is_string($str) OR $str == '')
+		{
+			return FALSE;
+		}
+		
 		return ! preg_match('/[^0-9]/', $str);
 	}	
 }
@@ -75,6 +80,11 @@
 {
 	function ctype_alnum($str)
 	{
+		if (! is_string($str) OR $str == '')
+		{
+			return FALSE;
+		}
+		
 		return ! preg_match('/[^0-9a-z]/i', $str);
 	}	
 }