diff --git a/users.php b/users.php
index 7d474b6..53b40c6 100644
--- a/users.php
+++ b/users.php
@@ -72,6 +72,10 @@ class users
       throw new Exception (dgettext("domframework", 
                                     "Invalid email provided : too short"),
                            500);
+    if (strpos ($lastname, ":") !== false)
+      throw new Exception (dgettext("domframework", 
+                                "Invalid email provided : colon forbidden"),
+                           500);
     return true;
   }
 
@@ -86,6 +90,10 @@ class users
       throw new Exception (dgettext("domframework", 
                                     "Invalid firstname provided : too short"),
                            500);
+    if (strpos ($firstname, ":") !== false)
+      throw new Exception (dgettext("domframework", 
+                                "Invalid firstname provided : colon forbidden"),
+                           500);
     return true;
   }
 
@@ -96,6 +104,10 @@ class users
       throw new Exception (dgettext("domframework", 
                                     "Invalid lastname provided : not a string"),
                            500);
+    if (strpos ($lastname, ":") !== false)
+      throw new Exception (dgettext("domframework", 
+                                "Invalid lastname provided : colon forbidden"),
+                           500);
     return true;
   }