diff --git a/libs/plugins/function.math.php b/libs/plugins/function.math.php
index f3ac3d4b..04391077 100644
--- a/libs/plugins/function.math.php
+++ b/libs/plugins/function.math.php
@@ -35,12 +35,12 @@ function smarty_function_math($params, &$smarty)
     }
 
     // match all vars in equation, make sure all are passed
-    preg_match_all("!([a-zA-Z][a-zA-Z0-9_]*)!",$equation, $match);
+    preg_match_all("!(?:0x[a-fA-F0-9]+)|([a-zA-Z][a-zA-Z0-9_]+)!",$equation, $match);
     $allowed_funcs = array('int','abs','ceil','cos','exp','floor','log','log10',
                            'max','min','pi','pow','rand','round','sin','sqrt','srand','tan');
     
     foreach($match[1] as $curr_var) {
-        if (!in_array($curr_var,array_keys($params)) && !in_array($curr_var, $allowed_funcs)) {
+        if ($curr_var && !in_array($curr_var, array_keys($params)) && !in_array($curr_var, $allowed_funcs)) {
             $smarty->trigger_error("math: function call $curr_var not allowed");
             return;
         }