diff --git a/Project.toml b/Project.toml
index ed964167..0d560601 100644
--- a/Project.toml
+++ b/Project.toml
@@ -43,7 +43,7 @@ ArrayInterface = "6, 7"
 ChainRulesCore = "0.8, 0.9, 0.10, 1"
 ConstructionBase = "1"
 ForwardDiff = "0.10"
-Functors = "0.4.4"
+Functors = "0.4.4, 0.5"
 GPUArrays = "8, 9, 10"
 LinearAlgebra = "1"
 Optimisers = "0.3"