diff --git a/server/netwrapper.py b/server/netwrapper.py
index 4146d2c..e33728e 100644
--- a/server/netwrapper.py
+++ b/server/netwrapper.py
@@ -31,7 +31,8 @@ class NetWrapper:
         return encrypted_msg
 
     def signRSAHeader(self, type: str, extradata: dict) -> (bytes, bytes):
-        header = json.dumps({'type': type, 'source': self.network.own_addr}.update(extradata)).encode('UTF-8')
+        mandatory = {'type': type, 'source': self.network.own_addr}
+        header = json.dumps({**mandatory, **extradata}).encode('UTF-8')
         h = SHA512.new(header)
         headersignature = pkcs1_15.new(self.serverPrivateKey).sign(h)
         return header, headersignature