diff --git a/Project.toml b/Project.toml
index 1a2d23b..eb21404 100644
--- a/Project.toml
+++ b/Project.toml
@@ -21,8 +21,9 @@ Reexport = "0.2, 1.0"
 julia = "1"
 
 [extras]
+ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 Combinatorics = "861a8166-3701-5b0c-9a16-15d98fcdc6aa"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Combinatorics", "Test"]
+test = ["ChainRulesCore", "Combinatorics", "Test"]