diff --git a/Project.toml b/Project.toml
index 2086dec3..cc643f52 100644
--- a/Project.toml
+++ b/Project.toml
@@ -11,6 +11,18 @@ Requires = "ae029012-a4dd-5104-9daa-d747884805df"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 Unicode = "4ec0a83e-493e-50e2-b9ac-8f72acf5a8f5"
 
+[weakdeps]
+JSON = "682c06a0-de6a-54ab-a142-c8b1cf79cde6"
+RecipesBase = "3cdcf5f2-1ef4-517c-9805-6587b60abb01"
+SentinelArrays = "91c51154-3ec4-41a3-a24f-3f23e20d615c"
+StructTypes = "856f2bd8-1eba-4b0a-8007-ebc267875bd4"
+
+[extensions]
+CategoricalArraysJSONExt = "JSON"
+CategoricalArraysRecipesBaseExt = "RecipesBase"
+CategoricalArraysSentinelArraysExt = "SentinelArrays"
+CategoricalArraysStructTypesExt = "StructTypes"
+
 [compat]
 DataAPI = "1.6"
 JSON = "0.15, 0.16, 0.17, 0.18, 0.19, 0.20, 0.21"
diff --git a/ext/CategoricalArraysJSONExt.jl b/ext/CategoricalArraysJSONExt.jl
new file mode 100644
index 00000000..86c0e67f
--- /dev/null
+++ b/ext/CategoricalArraysJSONExt.jl
@@ -0,0 +1,14 @@
+module CategoricalArraysJSONExt
+
+if isdefined(Base, :get_extension)
+    using CategoricalArrays
+    using JSON
+else
+    using ..CategoricalArrays
+    using ..JSON
+end
+
+# JSON of CategoricalValue is JSON of the value it refers to
+JSON.lower(x::CategoricalValue) = JSON.lower(unwrap(x))
+
+end
diff --git a/ext/CategoricalArraysRecipesBaseExt.jl b/ext/CategoricalArraysRecipesBaseExt.jl
new file mode 100644
index 00000000..2642f838
--- /dev/null
+++ b/ext/CategoricalArraysRecipesBaseExt.jl
@@ -0,0 +1,18 @@
+module CategoricalArraysRecipesBaseExt
+
+if isdefined(Base, :get_extension)
+    using CategoricalArrays
+    using RecipesBase
+else
+    using ..CategoricalArrays
+    using ..RecipesBase
+end
+
+RecipesBase.@recipe function f(::Type{T}, v::T) where T <: CategoricalValue
+    level_strings = [map(string, levels(v)); missing]
+    ticks --> eachindex(level_strings)
+    v -> ismissing(v) ? length(level_strings) : Int(CategoricalArrays.refcode(v)),
+    i -> level_strings[Int(i)]
+end
+
+end
diff --git a/ext/CategoricalArraysSentinelArraysExt.jl b/ext/CategoricalArraysSentinelArraysExt.jl
new file mode 100644
index 00000000..fd439bbd
--- /dev/null
+++ b/ext/CategoricalArraysSentinelArraysExt.jl
@@ -0,0 +1,21 @@
+module CategoricalArraysSentinelArraysExt
+
+if isdefined(Base, :get_extension)
+    using CategoricalArrays
+    using SentinelArrays
+else
+    using ..CategoricalArrays
+    using ..SentinelArrays
+end
+
+Base.copyto!(dest::CategoricalArrays.CatArrOrSub{<:Any, 1}, src::SentinelArrays.ChainedVector) =
+    copyto!(dest, 1, src, 1, length(src))
+Base.copyto!(dest::CategoricalArrays.CatArrOrSub{<:Any, 1}, dstart::Union{Signed, Unsigned},
+    src::SentinelArrays.ChainedVector, sstart::Union{Signed, Unsigned},
+    n::Union{Signed, Unsigned}) =
+    invoke(copyto!, Tuple{AbstractArray, Union{Signed, Unsigned},
+                        SentinelArrays.ChainedVector,
+                        Union{Signed, Unsigned}, Union{Signed, Unsigned}},
+        dest, dstart, src, sstart, n)
+
+end
diff --git a/ext/CategoricalArraysStructTypesExt.jl b/ext/CategoricalArraysStructTypesExt.jl
new file mode 100644
index 00000000..723ba8cf
--- /dev/null
+++ b/ext/CategoricalArraysStructTypesExt.jl
@@ -0,0 +1,44 @@
+module CategoricalArraysStructTypesExt
+
+if isdefined(Base, :get_extension)
+    using CategoricalArrays
+    using StructTypes
+else
+    using ..CategoricalArrays
+    using ..StructTypes
+end
+
+# define appropriate handlers for JSON3 interface
+StructTypes.StructType(x::CategoricalValue) = StructTypes.StructType(unwrap(x))
+StructTypes.StructType(::Type{<:CategoricalValue{T}}) where {T} = StructTypes.StructType(T)
+StructTypes.numbertype(::Type{<:CategoricalValue{T}}) where {T <: Number} = T
+StructTypes.construct(::Type{T}, x::CategoricalValue{T}) where {T} = T(unwrap(x))
+
+# JSON3 writing/reading
+StructTypes.StructType(::Type{<:CategoricalVector}) = StructTypes.ArrayType()
+
+StructTypes.construct(::Type{<:CategoricalArray}, A::AbstractVector) =
+    constructgeneral(A)
+StructTypes.construct(::Type{<:CategoricalArray}, A::Vector) =
+    constructgeneral(A)
+
+function constructgeneral(A)
+    if eltype(A) === Any
+        # unlike `replace`, broadcast narrows the type, which allows us to return small
+        # union eltypes (e.g. Union{String,Missing})
+        categorical(ifelse.(A .=== nothing, missing, A))
+    elseif eltype(A) >: Nothing
+        categorical(replace(A, nothing=>missing))
+    else
+        categorical(A)
+    end
+end
+
+StructTypes.construct(::Type{<:CategoricalArray{Union{Missing, T}}},
+                    A::AbstractVector) where {T} =
+    CategoricalArray{Union{Missing, T}}(replace(A, nothing=>missing))
+StructTypes.construct(::Type{<:CategoricalArray{Union{Missing, T}}},
+                    A::Vector) where {T} =
+    CategoricalArray{Union{Missing, T}}(replace(A, nothing=>missing))
+
+end
diff --git a/src/CategoricalArrays.jl b/src/CategoricalArrays.jl
index 967cc368..214a5d17 100644
--- a/src/CategoricalArrays.jl
+++ b/src/CategoricalArrays.jl
@@ -14,7 +14,6 @@ module CategoricalArrays
     using DataAPI
     using Missings
     using Printf
-    using Requires: @require
 
     # JuliaLang/julia#36810
     if VERSION < v"1.5.2"
@@ -35,66 +34,16 @@ module CategoricalArrays
 
     include("deprecated.jl")
 
-    function __init__()
-        @require JSON="682c06a0-de6a-54ab-a142-c8b1cf79cde6" begin
-            # JSON of CategoricalValue is JSON of the value it refers to
-            JSON.lower(x::CategoricalValue) = JSON.lower(unwrap(x))
-        end
-
-        @require RecipesBase="3cdcf5f2-1ef4-517c-9805-6587b60abb01" @eval begin
-            RecipesBase.@recipe function f(::Type{T}, v::T) where T <: CategoricalValue
-                level_strings = [map(string, levels(v)); missing]
-                ticks --> eachindex(level_strings)
-                v -> ismissing(v) ? length(level_strings) : Int(refcode(v)),
-                i -> level_strings[Int(i)]
-            end
-        end
-
-        @require SentinelArrays="91c51154-3ec4-41a3-a24f-3f23e20d615c" begin
-            copyto!(dest::CatArrOrSub{<:Any, 1}, src::SentinelArrays.ChainedVector) =
-                copyto!(dest, 1, src, 1, length(src))
-            copyto!(dest::CatArrOrSub{<:Any, 1}, dstart::Union{Signed, Unsigned},
-                    src::SentinelArrays.ChainedVector, sstart::Union{Signed, Unsigned},
-                    n::Union{Signed, Unsigned}) =
-                invoke(copyto!, Tuple{AbstractArray, Union{Signed, Unsigned},
-                                    SentinelArrays.ChainedVector,
-                                    Union{Signed, Unsigned}, Union{Signed, Unsigned}},
-                    dest, dstart, src, sstart, n)
-        end
-
-        @require StructTypes="856f2bd8-1eba-4b0a-8007-ebc267875bd4" begin
-            # define appropriate handlers for JSON3 interface
-            StructTypes.StructType(x::CategoricalValue) = StructTypes.StructType(unwrap(x))
-            StructTypes.StructType(::Type{<:CategoricalValue{T}}) where {T} = StructTypes.StructType(T)
-            StructTypes.numbertype(::Type{<:CategoricalValue{T}}) where {T <: Number} = T
-            StructTypes.construct(::Type{T}, x::CategoricalValue{T}) where {T} = T(unwrap(x))
-
-            # JSON3 writing/reading
-            StructTypes.StructType(::Type{<:CategoricalVector}) = StructTypes.ArrayType()
-
-            StructTypes.construct(::Type{<:CategoricalArray}, A::AbstractVector) =
-                constructgeneral(A)
-            StructTypes.construct(::Type{<:CategoricalArray}, A::Vector) =
-                constructgeneral(A)
-
-            function constructgeneral(A)
-                if eltype(A) === Any
-                    # unlike `replace`, broadcast narrows the type, which allows us to return small
-                    # union eltypes (e.g. Union{String,Missing})
-                    categorical(ifelse.(A .=== nothing, missing, A))
-                elseif eltype(A) >: Nothing
-                    categorical(replace(A, nothing=>missing))
-                else
-                    categorical(A)
-                end
-            end
+    if !isdefined(Base, :get_extension)
+        using Requires: @require
+    end
 
-            StructTypes.construct(::Type{<:CategoricalArray{Union{Missing, T}}},
-                                A::AbstractVector) where {T} =
-                CategoricalArray{Union{Missing, T}}(replace(A, nothing=>missing))
-            StructTypes.construct(::Type{<:CategoricalArray{Union{Missing, T}}},
-                                A::Vector) where {T} =
-                CategoricalArray{Union{Missing, T}}(replace(A, nothing=>missing))
+    @static if !isdefined(Base, :get_extension)
+        function __init__()
+            @require JSON="682c06a0-de6a-54ab-a142-c8b1cf79cde6" include("../ext/CategoricalArraysJSONExt.jl")
+            @require RecipesBase="3cdcf5f2-1ef4-517c-9805-6587b60abb01" include("../ext/CategoricalArraysRecipesBaseExt.jl")
+            @require SentinelArrays="91c51154-3ec4-41a3-a24f-3f23e20d615c" include("../ext/CategoricalArraysSentinelArraysExt.jl")
+            @require StructTypes="856f2bd8-1eba-4b0a-8007-ebc267875bd4" include("../ext/CategoricalArraysStructTypesExt.jl")
         end
     end
 end