diff --git a/Project.toml b/Project.toml
index 7700e37cf..ced2642ae 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "ChainRulesCore"
 uuid = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
-version = "0.9.17"
+version = "0.9.18"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
diff --git a/src/differentials/composite.jl b/src/differentials/composite.jl
index 98a56e259..5abbd31dd 100644
--- a/src/differentials/composite.jl
+++ b/src/differentials/composite.jl
@@ -82,6 +82,11 @@ end
 Base.keys(comp::Composite) = keys(backing(comp))
 Base.propertynames(comp::Composite) = propertynames(backing(comp))
 
+Base.haskey(comp::Composite, key) = haskey(backing(comp), key)
+if isdefined(Base, :hasproperty)
+    Base.hasproperty(comp::Composite, key::Symbol) = hasproperty(backing(comp), key)
+end
+
 Base.iterate(comp::Composite, args...) = iterate(backing(comp), args...)
 Base.length(comp::Composite) = length(backing(comp))
 Base.eltype(::Type{<:Composite{<:Any, T}}) where T = eltype(T)
diff --git a/test/differentials/composite.jl b/test/differentials/composite.jl
index cb872e9a3..b26ba5c13 100644
--- a/test/differentials/composite.jl
+++ b/test/differentials/composite.jl
@@ -48,6 +48,10 @@ end
     @testset "indexing, iterating, and properties" begin
         @test keys(Composite{Foo}(x=2.5)) == (:x,)
         @test propertynames(Composite{Foo}(x=2.5)) == (:x,)
+        @test haskey(Composite{Foo}(x=2.5), :x) == true
+        if isdefined(Base, :hasproperty)
+            @test hasproperty(Composite{Foo}(x=2.5), :y) == false
+        end
         @test Composite{Foo}(x=2.5).x == 2.5
 
         @test keys(Composite{Tuple{Float64,}}(2.0)) == Base.OneTo(1)
@@ -56,6 +60,10 @@ end
         @test getproperty(Composite{Tuple{Float64,}}(@thunk 2.0^2), 1) == 4.0
         @test getproperty(Composite{Tuple{Float64,}}(a=(@thunk 2.0^2),), :a) == 4.0
 
+        # TODO: uncomment this once https://github.com/JuliaLang/julia/issues/35516
+        @test_broken haskey(Composite{Tuple{Float64}}(2.0), 1) == true
+        @test_broken hasproperty(Composite{Tuple{Float64}}(2.0), 2) == false
+
         @test length(Composite{Foo}(x=2.5)) == 1
         @test length(Composite{Tuple{Float64,}}(2.0)) == 1