diff --git a/include/ac_common.php b/include/ac_common.php
index 88a286f6d..ea2b6d28f 100644
--- a/include/ac_common.php
+++ b/include/ac_common.php
@@ -72,7 +72,7 @@ function cmpDate ($p_date,$p_date_oth) {
  */
 function isNumber($p_int) {
   if ( strlen (trim($p_int)) == 0 ) return 0;
-  if (! ereg ("^[0-9]+$",$p_int) ) {
+  if (! ereg ("^-{0,1}[0-9]+.{0,1}[0-9]*$",$p_int) ) {
     return 0;
   } else {
     return 1;