diff --git a/Project.toml b/Project.toml
index c4936b855..2f334ffeb 100644
--- a/Project.toml
+++ b/Project.toml
@@ -15,7 +15,7 @@ Reexport = "0.2, 1"
 ReinforcementLearningBase = "0.9"
 ReinforcementLearningCore = "0.8"
 ReinforcementLearningEnvironments = "0.6"
-ReinforcementLearningZoo = "0.5"
+ReinforcementLearningZoo = "0.5, 0.4"
 julia = "1.6"
 
 [extras]