diff --git a/libp2p/security/noise/io.py b/libp2p/security/noise/io.py
index 327a5400..725c809b 100644
--- a/libp2p/security/noise/io.py
+++ b/libp2p/security/noise/io.py
@@ -72,7 +72,7 @@ class NoiseHandshakeReadWriter(BaseNoiseMsgReadWriter):
         return self.noise_state.write_message(data)
 
     def decrypt(self, data: bytes) -> bytes:
-        return self.noise_state.read_message(data)
+        return bytes(self.noise_state.read_message(data))
 
 
 class NoiseTransportReadWriter(BaseNoiseMsgReadWriter):
diff --git a/pyproject.toml b/pyproject.toml
index ef7ae331..9bbbec80 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -69,6 +69,10 @@ xfail_strict = true
 log_format = "%(levelname)8s  %(asctime)s  %(filename)20s  %(message)s"
 log_date_format = "%m-%d %H:%M:%S"
 
+markers = [
+  "slow: mark test as slow",
+]
+
 [tool.towncrier]
 # Read https://github.com/ethereum/py-libp2p/blob/main/newsfragments/README.md for instructions
 package = "libp2p"