diff --git a/Project.toml b/Project.toml
index 45e4671..1965947 100644
--- a/Project.toml
+++ b/Project.toml
@@ -28,7 +28,7 @@ Distributions = "0.25"
 DistributionsAD = "0.6"
 ExprTools = "0.1"
 ForwardDiff = "0.10"
-Functors = "0.4.3"
+Functors = "0.4.3, 0.5"
 julia = "1"
 
 [extras]