diff --git a/src/ADTypes.jl b/src/ADTypes.jl
index a30e6f2..2b2fca8 100644
--- a/src/ADTypes.jl
+++ b/src/ADTypes.jl
@@ -22,10 +22,12 @@ end
 
 AutoFiniteDifferences(; fdm = nothing) = AutoFiniteDifferences(fdm)
 
-struct AutoForwardDiff{chunksize} <: AbstractADType end
+struct AutoForwardDiff{chunksize,T} <: AbstractADType
+    tag::T
+end
 
-function AutoForwardDiff(chunksize = nothing)
-    AutoForwardDiff{chunksize}()
+function AutoForwardDiff(; chunksize = nothing, tag = nothing)
+    AutoForwardDiff{chunksize,typeof(tag)}(tag)
 end
 
 struct AutoReverseDiff <: AbstractADType
@@ -55,10 +57,12 @@ end
 
 struct AutoSparseFiniteDiff <: AbstractADType end
 
-struct AutoSparseForwardDiff{chunksize} <: AbstractADType end
+struct AutoSparseForwardDiff{chunksize,T} <: AbstractADType
+    tag::T
+end
 
-function AutoSparseForwardDiff(chunksize = nothing)
-    AutoSparseForwardDiff{chunksize}()
+function AutoSparseForwardDiff(; chunksize = nothing, tag = nothing)
+    AutoSparseForwardDiff{chunksize,typeof(tag)}(tag)
 end
 
 export AutoFiniteDiff, AutoFiniteDifferences, AutoForwardDiff, AutoReverseDiff, AutoZygote, AutoEnzyme, AutoTracker, AutoModelingToolkit, AutoSparseFiniteDiff, AutoSparseForwardDiff
diff --git a/test/runtests.jl b/test/runtests.jl
index 3944cf3..d309cf6 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -1,6 +1,8 @@
 using ADTypes
 using Test
 
+struct CustomTag end
+
 @testset "ADTypes.jl" begin
     adtype = AutoFiniteDiff()
     @test adtype isa ADTypes.AbstractADType
@@ -22,11 +24,12 @@ using Test
 
     adtype = AutoForwardDiff()
     @test adtype isa ADTypes.AbstractADType
-    @test adtype isa AutoForwardDiff{nothing}
 
-    adtype = AutoForwardDiff(10)
+    @test adtype isa AutoForwardDiff{nothing,Nothing}
+
+    adtype = AutoForwardDiff(; chunksize = 10, tag = CustomTag())
     @test adtype isa ADTypes.AbstractADType
-    @test adtype isa AutoForwardDiff{10}
+    @test adtype isa AutoForwardDiff{10,CustomTag}
 
     adtype = AutoReverseDiff()
     @test adtype isa ADTypes.AbstractADType
@@ -46,15 +49,13 @@ using Test
     @test adtype isa ADTypes.AbstractADType
     @test adtype isa AutoTracker
 
-    adtype = AutoEnzyme()
+    adtype = AutoSparseForwardDiff()
     @test adtype isa ADTypes.AbstractADType
-    @test adtype isa AutoEnzyme{Nothing}
+    @test adtype isa AutoSparseForwardDiff{nothing,Nothing}
 
-    # In practice, you would rather specify a
-    # `mode::Enzyme.Mode`, e.g. `Enzyme.Reverse` or `Enzyme.Forward`
-    adtype = AutoEnzyme(; mode = Val(:Reverse))
+    adtype = AutoSparseForwardDiff(; chunksize = 10, tag = CustomTag())
     @test adtype isa ADTypes.AbstractADType
-    @test adtype isa AutoEnzyme{Val{:Reverse}}
+    @test adtype isa AutoSparseForwardDiff{10,CustomTag}
 
     adtype = AutoModelingToolkit()
     @test adtype isa ADTypes.AbstractADType
@@ -76,7 +77,13 @@ using Test
     @test adtype isa ADTypes.AbstractADType
     @test adtype isa AutoSparseForwardDiff{nothing}
 
-    adtype = AutoSparseForwardDiff(10)
+    adtype = AutoEnzyme()
+    @test adtype isa ADTypes.AbstractADType
+    @test adtype isa AutoEnzyme{Nothing}
+
+    # In practice, you would rather specify a
+    # `mode::Enzyme.Mode`, e.g. `Enzyme.Reverse` or `Enzyme.Forward`
+    adtype = AutoEnzyme(; mode = Val(:Reverse))
     @test adtype isa ADTypes.AbstractADType
-    @test adtype isa AutoSparseForwardDiff{10}
+    @test adtype isa AutoEnzyme{Val{:Reverse}}
 end