diff --git a/Project.toml b/Project.toml
index ca5f9c42..53be8f8a 100644
--- a/Project.toml
+++ b/Project.toml
@@ -4,6 +4,7 @@ authors = ["Guillaume Dalle"]
 version = "0.4.0"
 
 [deps]
+ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 DensityInterface = "b429d917-457f-4dbc-8f4c-0cc954292b1d"
 Distributions = "31c24e10-a181-5473-b8eb-7969acd0382f"
 DocStringExtensions = "ffbed154-4ef7-542d-bbb7-c09d3a79fcae"
diff --git a/src/HiddenMarkovModels.jl b/src/HiddenMarkovModels.jl
index 58fb17dd..715efb9d 100644
--- a/src/HiddenMarkovModels.jl
+++ b/src/HiddenMarkovModels.jl
@@ -49,13 +49,11 @@ include("inference/baum_welch.jl")
 include("utils/HMMTest.jl")
 
 if !isdefined(Base, :get_extension)
+    include("../ext/HiddenMarkovModelsChainRulesCoreExt.jl")
     function __init__()
         @require HMMBase = "b2b3ca75-8444-5ffa-85e6-af70e2b64fe7" include(
             "../ext/HiddenMarkovModelsHMMBaseExt.jl"
         )
-        @require ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4" include(
-            "../ext/HiddenMarkovModelsChainRulesCoreExt.jl"
-        )
     end
 end