diff --git a/python/requirements.txt b/python/requirements.txt
index 51e7b38fd..df338cb12 100644
--- a/python/requirements.txt
+++ b/python/requirements.txt
@@ -55,7 +55,6 @@ mypy
 networkx
 numba
 openpyxl
-pettingzoo>=1.4.0
 Pillow; platform_system != "Windows"
 pygments
 pytest==5.4.3
diff --git a/python/requirements_rllib.txt b/python/requirements_rllib.txt
index 6eb506be3..442e3db2f 100644
--- a/python/requirements_rllib.txt
+++ b/python/requirements_rllib.txt
@@ -5,3 +5,5 @@ torch>=1.6.0
 # Version requirement to match Tune
 torchvision>=0.6.0
 smart_open
+# For tests on PettingZoo's multi-agent envs.
+pettingzoo>=1.4.0