diff --git a/Project.toml b/Project.toml
index 6592da9..5a1497d 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "Roots"
 uuid = "f2b01f46-fcfa-551c-844a-d8ac1e96c665"
-version = "2.1.8"
+version = "2.2.0"
 
 [deps]
 Accessors = "7d9f7c33-5ae7-4f3b-8dc6-eff91059b697"
@@ -9,12 +9,14 @@ CommonSolve = "38540f10-b2f7-11e9-35d8-d573e4eb0ff2"
 Printf = "de0858da-6303-5e67-8744-51eddeeeb8d7"
 
 [weakdeps]
+ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 ForwardDiff = "f6369f11-7733-5829-9624-2563aa707210"
 IntervalRootFinding = "d2bf35a9-74e0-55ec-b149-d360ff49b807"
 SymPy = "24249f21-da20-56a4-8eb1-6a02cf4ae2e6"
 SymPyPythonCall = "bc8888f7-b21e-4b7c-a06a-5d9c9496438c"
 
 [extensions]
+RootsChainRulesCoreExt = "ChainRulesCore"
 RootsForwardDiffExt = "ForwardDiff"
 RootsIntervalRootFindingExt = "IntervalRootFinding"
 RootsSymPyExt = "SymPy"
diff --git a/src/chain_rules.jl b/ext/RootsChainRulesCoreExt.jl
similarity index 91%
rename from src/chain_rules.jl
rename to ext/RootsChainRulesCoreExt.jl
index 9c1b374..c45dabb 100644
--- a/src/chain_rules.jl
+++ b/ext/RootsChainRulesCoreExt.jl
@@ -1,3 +1,8 @@
+module RootsChainRulesCoreExt
+
+using Roots
+import ChainRulesCore
+
 # View find_zero as solving `f(x, p) = 0` for `xᵅ(p)`.
 # This is implicitly defined. By the implicit function theorem, we have:
 # ∇f = 0 => ∂/∂ₓ f(xᵅ, p) ⋅ ∂xᵅ/∂ₚ + ∂/∂ₚf(x\^α, p) ⋅ I = 0
@@ -15,7 +20,6 @@
 # that is fixable.)
 
 # this assumes a function and a parameter `p` passed in
-import ChainRulesCore: Tangent, NoTangent, frule, rrule
 function ChainRulesCore.frule(
     config::ChainRulesCore.RuleConfig{>:ChainRulesCore.HasForwardsMode},
     (_, _, _, Δp),
@@ -42,17 +46,17 @@ ChainRulesCore.frule(
     config::ChainRulesCore.RuleConfig{>:ChainRulesCore.HasForwardsMode},
     xdots,
     ::typeof(solve),
-    ZP::Roots.ZeroProblem,
+    ZP::ZeroProblem,
     M::Roots.AbstractUnivariateZeroMethod,
     ::Nothing;
     kwargs...,
-) = frule(config, xdots, solve, ZP, M; kwargs...)
+) = ChainRulesCore.frule(config, xdots, solve, ZP, M; kwargs...)
 
 function ChainRulesCore.frule(
     config::ChainRulesCore.RuleConfig{>:ChainRulesCore.HasForwardsMode},
     (_, Δq, _),
     ::typeof(solve),
-    ZP::Roots.ZeroProblem,
+    ZP::ZeroProblem,
     M::Roots.AbstractUnivariateZeroMethod;
     kwargs...,
 )
@@ -61,12 +65,12 @@ function ChainRulesCore.frule(
     zprob2 = ZeroProblem(|>, ZP.x₀)
     nms = fieldnames(typeof(foo))
     nt = NamedTuple{nms}(getfield(foo, n) for n in nms)
-    dfoo = Tangent{typeof(foo)}(; nt...)
+    dfoo = ChainRulesCore.Tangent{typeof(foo)}(; nt...)
 
-    return frule(
+    return ChainRulesCore.frule(
         config,
-        (NoTangent(), NoTangent(), NoTangent(), dfoo),
-        Roots.solve,
+        (ChainRulesCore.NoTangent(), ChainRulesCore.NoTangent(), ChainRulesCore.NoTangent(), dfoo),
+        solve,
         zprob2,
         M,
         foo,
@@ -146,3 +150,5 @@ function ChainRulesCore.rrule(
 
     return xᵅ, pullback_solve_ZeroProblem
 end
+
+end # module
diff --git a/src/Roots.jl b/src/Roots.jl
index 35ddf0d..8dea221 100644
--- a/src/Roots.jl
+++ b/src/Roots.jl
@@ -22,7 +22,6 @@ using Printf
 import CommonSolve
 import CommonSolve: solve, solve!, init
 using Accessors
-import ChainRulesCore
 
 export fzero, fzeros, secant_method
 
@@ -53,7 +52,6 @@ include("functions.jl")
 include("trace.jl")
 include("find_zero.jl")
 include("hybrid.jl")
-include("chain_rules.jl")
 
 include("Bracketing/bracketing.jl")
 include("Bracketing/bisection.jl")
@@ -83,4 +81,8 @@ include("find_zeros.jl")
 include("simple.jl")
 include("alternative_interfaces.jl")
 
+if !isdefined(Base, :get_extension)
+    include("../ext/RootsChainRulesCoreExt.jl")
+end
+
 end