diff --git a/fedmsg_migration_tools/bridges.py b/fedmsg_migration_tools/bridges.py
index fb9bf48..634a19e 100644
--- a/fedmsg_migration_tools/bridges.py
+++ b/fedmsg_migration_tools/bridges.py
@@ -18,6 +18,7 @@
 import datetime
 import json
 import logging
+import re
 import socket
 import time
 
@@ -31,6 +32,9 @@
 _log = logging.getLogger(__name__)
 
 
+YEAR_PREFIX_RE = re.compile("^[0-9]{4}-")
+
+
 def zmq_to_amqp(exchange, zmq_endpoints, topics):
     """
     Connect to a set of ZeroMQ PUB sockets and re-publish the messages to an AMQP
@@ -186,13 +190,14 @@ def __call__(self, message):
         # wrap messages bridged back into ZMQ with it so old consumers don't
         # explode with KeyErrors.
         self._message_counter += 1
+        msg_id = message.id
+        if not YEAR_PREFIX_RE.match(msg_id[:5]):
+            msg_id = "{}-{}".format(datetime.datetime.utcnow().year, msg_id)
         wrapped_body = {
             "topic": message.topic,
             "msg": message._body,
             "timestamp": int(time.time()),
-            "msg_id": "{y}-{id}".format(
-                y=datetime.datetime.utcnow().year, id=message.id
-            ),
+            "msg_id": msg_id,
             "i": self._message_counter,
             "username": "amqp-bridge",
         }
diff --git a/fedmsg_migration_tools/tests/test_bridges.py b/fedmsg_migration_tools/tests/test_bridges.py
index dd12a5d..dbe6a6a 100644
--- a/fedmsg_migration_tools/tests/test_bridges.py
+++ b/fedmsg_migration_tools/tests/test_bridges.py
@@ -186,3 +186,17 @@ def test_local_or_remote_publish(self):
         with mock.patch.dict("fedmsg_migration_tools.bridges.fm_config.conf", conf):
             zmq_bridge = bridges.AmqpToZmq()
         zmq_bridge.pub_socket.connect.assert_called_with("dummy_endpoint")
+
+    @mock.patch("fedmsg_migration_tools.bridges.zmq.Context", mock.Mock())
+    def test_double_year_prefix(self):
+        """Assert that the year prefix is not added if it is already present."""
+        year = datetime.datetime.utcnow().year
+        zmq_bridge = bridges.AmqpToZmq()
+        msg = message.Message(topic="my.topic", body={"my": "message"})
+        # Add a year prefix to the original message.
+        msg.id = "{}-{}".format(year, msg.id)
+        zmq_bridge(msg)
+        zmq_bridge.pub_socket.send_multipart.assert_called_once()
+        body = zmq_bridge.pub_socket.send_multipart.call_args_list[-1][0][0][1]
+        # No year prefix should been added.
+        assert json.loads(body.decode("utf-8"))["msg_id"] == msg.id