diff --git a/www/extras/inputCheck.js b/www/extras/inputCheck.js
index a9f1701ca..49ec53942 100644
--- a/www/extras/inputCheck.js
+++ b/www/extras/inputCheck.js
@@ -4,9 +4,9 @@ function doInputCheck(field,valid) {
         for (var i=0; i<field.value.length; i++) {
         	temp = "" + field.value.substring(i, i+1);
                 if (valid.indexOf(temp) == "-1") ok = "no";
-        }
-        if (ok == "no") {
-                field.value = field.value.substring(0, (field.value.length) - 1);
+        
+        	if (ok == "no") {
+        	 field.value = field.value.substring(0, i);
+		}
         }
 }
-