diff --git a/Project.toml b/Project.toml
index 9224c730..fa861419 100644
--- a/Project.toml
+++ b/Project.toml
@@ -34,6 +34,7 @@ ForwardDiff = "0.10.6"
 MacroTools = "0.5"
 NaNMath = "0.3"
 PDMats = "0.9"
+Requires = "1"
 SpecialFunctions = "0.8, 0.9, 0.10"
 StatsBase = "0.32, 0.33"
 StaticArrays = "0.12"