--- a/mail/components/im/content/imconversation.xml
+++ b/mail/components/im/content/imconversation.xml
@@ -941,20 +941,20 @@
            this._activeBuddies[aBuddy.name] = true;
          }
 
          if (!this.tab.selected)
            return;
 
          // Is aOldName is not null, then we are renaming the buddy
          if (!this._hasBuddy(aOldName))
-           throw "Updating a chat buddy that does not exist?!";
+           throw "Updating a chat buddy that does not exist: " + aOldName;
 
          if (this._hasBuddy(name))
-           throw "Updating a chat buddy to an already existing one?!";
+           throw "Updating a chat buddy to an already existing one: " + name;
 
          var item = this.buddies[aOldName];
          item.chatBuddy = aBuddy;
          delete this.buddies[aOldName];
          this.buddies[name] = item;
          item.setAttribute("label", name);
 
          // Move this item to the right position if its name changed