diff --git a/mobile.webservice.php b/mobile.webservice.php
index 3a85b29..c7dea92 100644
--- a/mobile.webservice.php
+++ b/mobile.webservice.php
@@ -80,8 +80,11 @@ abstract class WebService
         $nbArgs = $rm->getNumberOfParameters();
 
         /* Check the number of arguments. */
-        if ($nbArgs != $nbParams && $nbArgsFix != $nbParams) {
-            throw new WebException ("CallArgNumber", "you must provide " . $nbArgsFix . " arguments", 4);
+        if ($nbParams < $nbArgsFix) {
+            throw new WebException ("CallArgNumber", "you must provide at least " . $nbArgsFix . " arguments", 4);
+        }
+        if ($nbParams > $nbArgs) {
+            throw new WebException ("CallArgNumber", "you must provide at most " . $nbArgs . " arguments", 4);
         }
 
         $this->log("Calling '".$this->func."'");