diff --git a/model/ns3gym/requirements.txt b/model/ns3gym/requirements.txt
index 6fa1f2327..26ca3fb93 100644
--- a/model/ns3gym/requirements.txt
+++ b/model/ns3gym/requirements.txt
@@ -1,4 +1,4 @@
 pyzmq
 numpy
-protobuf
-gym
\ No newline at end of file
+protobuf==3.20.4
+gym
diff --git a/model/ns3gym/setup.py b/model/ns3gym/setup.py
index 2a3bc00be..a14e7b0e5 100644
--- a/model/ns3gym/setup.py
+++ b/model/ns3gym/setup.py
@@ -27,6 +27,6 @@ def readme():
     description='OpenAI Gym meets ns-3',
     long_description='OpenAI Gym meets ns-3',
     keywords='openAI gym, ML, RL, ns-3',
-    install_requires=['pyzmq', 'numpy', 'protobuf', 'gym'],
+    install_requires=['pyzmq', 'numpy', 'protobuf==3.20.4', 'gym'],
     extras_require={},
 )