diff --git a/server/index.php b/server/index.php
index a1baff8..3b43672 100644
--- a/server/index.php
+++ b/server/index.php
@@ -102,8 +102,8 @@ else
         }
     }
         echo "</select>\n";
-        echo '  <b>Master key </b> <input id="master_key" type="password" onkeypress="if (event.keyCode == 13) update_master_key();"/>';
-        echo "<input type=\"button\" value=\"See\" onclick=\"update_master_key();\" />" . "\n";
+        echo '  <b>Master key </b> <input id="master_key" type="password" onkeypress="if (event.keyCode == 13) update_master_key(true);"/>';
+        echo "<input type=\"button\" value=\"See\" onclick=\"update_master_key(true);\" />" . "\n";
 
         if (!isset($_SERVER['HTTPS']))
    echo "<div id=\"addon_address\">Current addon address is : http://" . $_SERVER['SERVER_NAME'] . "/" . $user . "</div>\n";
diff --git a/server/ressources/gpass.js b/server/ressources/gpass.js
index 88e363b..d8cdf7f 100755
--- a/server/ressources/gpass.js
+++ b/server/ressources/gpass.js
@@ -219,10 +219,18 @@ function update_stats()
     div.appendChild(document.createElement("br"));
 }
 
-function change_master_key()
+function change_master_key(warning_unciphered)
 {
+    var nb_unciphered = 0;
     for(i=0; i<passwords.length; i++)
-	passwords[i].decrypt(current_mkey);
+    {
+	if (passwords[i].decrypt(current_mkey))
+	    nb_unciphered++;
+    }
+
+
+    if (!nb_unciphered && warning_unciphered)
+	alert("No password unciphered with this master key !");
 
     password_div = document.getElementById("passwords");
     password_div.removeAllChilds();
@@ -326,10 +334,13 @@ function change_master_key()
 	}
     }
 
+    input = document.getElementById("master_key");
+    input.value = "";
+
     update_stats();
 }
 
-function update_master_key()
+function update_master_key(warning_unciphered)
 {
     user = select_widget.options[select_widget.selectedIndex].value;
 
@@ -352,7 +363,7 @@ function update_master_key()
     if (current_mkey != "")
 	current_mkey = derive_mkey(current_user, current_mkey);
 
-    change_master_key();
+    change_master_key(warning_unciphered);
 }
 
 function start()
@@ -361,7 +372,7 @@ function start()
     
     if (select_widget == null) return;
 
-    return update_master_key();
+    return update_master_key(false);
 }
 
 function add_password_server(user, pentry)
@@ -505,7 +516,7 @@ function add_password()
     
     passwords.push(pentry);
 
-    change_master_key();
+    change_master_key(false);
 
     for(i=0; i<inputs.length; i++)
     {