diff --git a/squinnondation/hazel.py b/squinnondation/hazel.py
index 4af8e31..5bd436d 100644
--- a/squinnondation/hazel.py
+++ b/squinnondation/hazel.py
@@ -128,13 +128,21 @@ class Squirrel(Hazelnut):
         creates a new hazelnut.
         """
         if (address, port) in self.hazelnuts:
-            self.add_system_message(str(self.hazelnuts))
             return self.hazelnuts[(address, port)]
         hazelnut = Hazelnut(address=address, port=port)
         self.hazelnuts[(address, port)] = hazelnut
-        self.add_system_message(str(self.hazelnuts))
         return hazelnut
 
+    def find_hazelnut_by_id(self, hazel_id: int) -> Hazelnut:
+        """
+        Retrieve the hazelnut that is known by its id. Return None if it is unknown.
+        The given identifier must be positive.
+        """
+        if hazel_id > 0:
+            for hazelnut in self.hazelnuts.values():
+                if hazelnut.id == hazel_id:
+                    return hazelnut
+
     def send_packet(self, client: Hazelnut, pkt: Packet) -> int:
         """
         Send a formatted packet to a client.
diff --git a/squinnondation/messages.py b/squinnondation/messages.py
index f938c66..7ce7d1a 100644
--- a/squinnondation/messages.py
+++ b/squinnondation/messages.py
@@ -12,7 +12,6 @@ import time
 class TLV:
     """
     The Tag-Length-Value contains the different type of data that can be sent.
-    TODO: add subclasses for each type of TLV
     """
     type: int
     length: int
@@ -159,6 +158,14 @@ class HelloTLV(TLV):
 
     def handle(self, squirrel: Any, sender: Any) -> None:
         time_h = time.time()
+
+        if sender.id > 0 and sender.id != self.source_id:
+            squirrel.send_packet(sender, Packet.construct(WarningTLV.construct(
+                f"You were known as the ID {sender.id}, but you declared that you have the ID {self.source_id}.")))
+            squirrel.add_system_message(f"A client known as the id {sender.id} declared that it uses "
+                                        f"the id {self.source_id}.")
+            sender.id = self.source_id
+
         if not sender.active:
             sender.id = self.source_id  # The sender we are given misses an id
             time_hl = time.time()
@@ -167,13 +174,6 @@ class HelloTLV(TLV):
         if self.is_long and self.dest_id == squirrel.id:
             time_hl = time.time()
 
-        if sender.id != self.source_id:
-            squirrel.send_packet(sender, Packet.construct(WarningTLV.construct(
-                f"You were known as the ID {sender.id}, but you declared that you have the ID {self.source_id}.")))
-            squirrel.add_system_message(f"A client known as the id {sender.id} declared that it uses "
-                                        f"the id {self.source_id}.")
-            sender.id = self.source_id
-
         # Add entry to/actualize the active hazelnuts dictionnary
         sender.last_hello_time = time_h
         sender.last_long_hello_time = time_hl
@@ -296,13 +296,15 @@ class DataTLV(TLV):
                 "Unable to retrieve your username. Please use the syntax 'nickname: message'")))
         else:
             nickname = nickname_match.group(1)
-            if sender.nickname is None:
-                sender.nickname = nickname
-            elif sender.nickname != nickname:
-                squirrel.send_packet(sender, Packet.construct(WarningTLV.construct(
-                    "It seems that you used two different nicknames. "
-                    f"Known nickname: {sender.nickname}, found: {nickname}")))
-                sender.nickname = nickname
+            author = squirrel.find_hazelnut_by_id(self.sender_id)
+            if author:
+                if author.nickname is None:
+                    author.nickname = nickname
+                elif author.nickname != nickname:
+                    squirrel.send_packet(author, Packet.construct(WarningTLV.construct(
+                        "It seems that you used two different nicknames. "
+                        f"Known nickname: {author.nickname}, found: {nickname}")))
+                    author.nickname = nickname
 
     @staticmethod
     def construct(message: str, squirrel: Any) -> "DataTLV":