diff --git a/docs/src/intset.md b/docs/src/intset.md
index 3057dbf1..be2b3509 100644
--- a/docs/src/intset.md
+++ b/docs/src/intset.md
@@ -1,6 +1,6 @@
 # DataStructures.IntSet
 
-`DataStructures.IntSet` is a drop-in replacement for the Base `BitSet`
+`DataStructures.IntSet` (`<: AbstractSet{Int}`) is a drop-in replacement for the Base `BitSet`
 type. It efficiently stores dense collections of small non-negative
 `Int`s as a sorted set. The constructor `IntSet([itr])` constructs a
 sorted set of the integers generated by the given iterable object, or an
diff --git a/docs/src/sparse_int_set.md b/docs/src/sparse_int_set.md
index 452318b6..ddf13b0c 100644
--- a/docs/src/sparse_int_set.md
+++ b/docs/src/sparse_int_set.md
@@ -1,5 +1,7 @@
 # DataStructures.SparseIntSet
 
+`SparseIntSet` is an `AbstractSet{Int}` with a packed representation.
+
 Implementation of a __Sparse Integer Set__, for background see [Sparse Sets](https://www.computist.xyz/2018/06/sparse-sets.html).
 Only positive non-zero `Int`s are allowed inside the set.
 The idea is to have one **packed** `Vector` storing all the `Int`s contained in the set as to allow for fast iteration, and a sparse, paged **reverse** `Vector` with the position of a particular `Int` inside the **packed** `Vector`. This allows for very fast iteration, insertion and deletion of indices.
diff --git a/src/int_set.jl b/src/int_set.jl
index ba1c6f5d..65d10ef9 100644
--- a/src/int_set.jl
+++ b/src/int_set.jl
@@ -1,6 +1,6 @@
 # This file was a part of Julia. License is MIT: http://julialang.org/license
 
-mutable struct IntSet
+mutable struct IntSet <: AbstractSet{Int}
     bits::BitVector
     inverse::Bool
     IntSet() = new(falses(256), false)
@@ -8,6 +8,9 @@ end
 IntSet(itr) = union!(IntSet(), itr)
 
 Base.empty(s::IntSet) = IntSet()
+Base.emptymutable(::IntSet, ::Type{Int}=Int) = IntSet()
+Base.copymutable(s::IntSet) = copy(s)
+Base.filter!(f, s::IntSet) = Base.unsafe_filter!(f, s)
 Base.copy(s1::IntSet) = copy!(IntSet(), s1)
 function Base.copy!(to::IntSet, from::IntSet)
     resize!(to.bits, length(from.bits))
@@ -133,6 +136,7 @@ end
 
 Base.symdiff(s::IntSet, ns) = symdiff!(copy(s), ns)
 Base.symdiff!(s::IntSet, ns) = (for n in ns; symdiff!(s, n); end; s)
+Base.symdiff!(s::IntSet, ns::AbstractSet) = (for n in ns; symdiff!(s, n); end; s)
 function Base.symdiff!(s::IntSet, n::Integer)
     0 <= n < typemax(Int) || throw(ArgumentError(_intset_bounds_err_msg))
     val = (n in s) ⊻ !s.inverse
diff --git a/src/sparse_int_set.jl b/src/sparse_int_set.jl
index c7b1001f..9eae634b 100644
--- a/src/sparse_int_set.jl
+++ b/src/sparse_int_set.jl
@@ -2,7 +2,7 @@ const INT_PER_PAGE = div(ccall(:jl_getpagesize, Clong, ()), sizeof(Int))
 # we use this to mark pages not in use, it must never be written to.
 const NULL_INT_PAGE = Vector{Int}()
 
-mutable struct SparseIntSet
+mutable struct SparseIntSet <: AbstractSet{Int}
     packed ::Vector{Int}
     reverse::Vector{Vector{Int}}
     counters::Vector{Int}  # counts the number of real elements in each page of reverse.
@@ -15,6 +15,9 @@ SparseIntSet(indices) = union!(SparseIntSet(), indices)
 Base.eltype(::Type{SparseIntSet}) = Int
 
 Base.empty(::SparseIntSet) = SparseIntSet()
+Base.emptymutable(::SparseIntSet, ::Type{Int}=Int) = SparseIntSet()
+Base.copymutable(s::SparseIntSet) = copy(s)
+Base.filter!(f, s::SparseIntSet) = Base.unsafe_filter!(f, s)
 
 function Base.empty!(s::SparseIntSet)
     empty!(s.packed)
@@ -143,6 +146,7 @@ end
     return in(id, s) ? (@inbounds pop!(s, id)) : default
 end
 Base.popfirst!(s::SparseIntSet) = pop!(s, first(s))
+Base.delete!(s::SparseIntSet, id::Integer) = (pop!(s, id, nothing); s)
 
 @inline Base.iterate(set::SparseIntSet, args...) = iterate(set.packed, args...)
 
@@ -170,6 +174,7 @@ Base.intersect!(s1::SparseIntSet, ss...) = intersect!(s1, intersect(ss...))
 
 #Is there a more performant way to do this?
 Base.intersect!(s1::SparseIntSet, ns) = copy!(s1, intersect(s1, ns))
+Base.intersect!(s1::SparseIntSet, ns::AbstractSet) = copy!(s1, intersect(s1, ns))
 
 Base.setdiff(s::SparseIntSet, ns) = setdiff!(copy(s), ns)
 function Base.setdiff!(s::SparseIntSet, ns)
diff --git a/test/test_int_set.jl b/test/test_int_set.jl
index 6606e794..e02a12a0 100644
--- a/test/test_int_set.jl
+++ b/test/test_int_set.jl
@@ -313,4 +313,65 @@ import DataStructures: IntSet
         show(IOBuffer(), complement(IntSet()))
     end
 
+
+    @testset "AbstractSet" begin
+        @test IntSet([1, 2]) isa AbstractSet{Int}
+        @test IntSet() isa AbstractSet{Int}
+
+        # Generic AbstractSet algorithms dispatch on IntSet
+        @test issetequal(IntSet([1, 2]), IntSet([2, 1]))
+        @test isdisjoint(IntSet([1]), IntSet([2]))
+        @test !isdisjoint(IntSet([1, 2]), IntSet([2, 3]))
+        @test IntSet([1]) ⊆ Set([1, 2])
+        @test Set([1]) ⊆ IntSet([1, 2])
+
+        # Cross-type equality becomes available via AbstractSet fallbacks
+        @test IntSet([1, 2]) == Set([1, 2])
+        @test IntSet([1, 2]) == SparseIntSet([1, 2])
+
+        # Derived operations stay within the type rather than degrading to Set
+        @test filter(isodd, IntSet([1, 2, 3])) isa IntSet
+        @test filter(isodd, IntSet([1, 2, 3])) == IntSet([1, 3])
+        @test filter(_ -> false, IntSet([1, 2])) isa IntSet
+        @test isempty(filter(_ -> false, IntSet([1, 2])))
+        @test setdiff(IntSet([1, 2, 3]), [2]) isa IntSet
+        @test setdiff(IntSet([1, 2, 3]), [2]) == IntSet([1, 3])
+        @test setdiff(IntSet([1, 2, 3]), IntSet([2])) isa IntSet
+
+        # filter! / intersect! with AbstractSet (Base uses filter!(in(s2), s))
+        s = IntSet([1, 2, 3])
+        filter!(isodd, s)
+        @test s == IntSet([1, 3])
+        s = IntSet([1, 2, 3])
+        intersect!(s, Set([2, 3, 4]))
+        @test s == IntSet([2, 3])
+        s = IntSet([1])
+        union!(s, Set([2]))
+        @test s == IntSet([1, 2])
+
+        # Same-type equality and ordering still win on specificity
+        @test IntSet([1]) == IntSet([1])
+        @test IntSet([1]) < IntSet([1, 2])
+        @test IntSet([1, 2]) <= IntSet([1, 2])
+
+        # symdiff! with an AbstractSet argument resolves unambiguously
+        @test symdiff!(IntSet([1, 2, 3]), Set([2, 4])) == IntSet([1, 3, 4])
+
+        # Complement remains IntSet <: AbstractSet
+        c = complement(IntSet([0, 1, 2]))
+        @test c isa IntSet
+        @test c isa AbstractSet{Int}
+        @test 3 in c
+        @test !(1 in c)
+
+        # emptymutable / copymutable keep type
+        @test Base.emptymutable(IntSet([1])) isa IntSet
+        s = IntSet([1, 2])
+        cpy = Base.copymutable(s)
+        push!(cpy, 9)
+        @test 9 in cpy
+        @test !(9 in s)
+    end
+
+
 end # @testset IntSet
diff --git a/test/test_sparse_int_set.jl b/test/test_sparse_int_set.jl
index b794a2cf..d64bb6de 100644
--- a/test/test_sparse_int_set.jl
+++ b/test/test_sparse_int_set.jl
@@ -1,5 +1,5 @@
 using DataStructures, Test
-import DataStructures: SparseIntSet
+import DataStructures: SparseIntSet, IntSet
 
 @testset "SparseIntSet" begin
     @testset "Construction, collect" begin
@@ -189,4 +189,49 @@ import DataStructures: SparseIntSet
             @test zip() isa Iterators.Zip  # issue 621
         end
 
+
+    @testset "AbstractSet" begin
+        @test SparseIntSet([1, 2]) isa AbstractSet{Int}
+        @test SparseIntSet() isa AbstractSet{Int}
+
+        @test issetequal(SparseIntSet([1, 2]), SparseIntSet([2, 1]))
+        @test isdisjoint(SparseIntSet([1]), SparseIntSet([2]))
+        @test !isdisjoint(SparseIntSet([1, 2]), SparseIntSet([2, 3]))
+        @test SparseIntSet([1]) ⊆ Set([1, 2])
+        @test Set([1]) ⊆ SparseIntSet([1, 2])
+
+        @test SparseIntSet([1, 2]) == Set([1, 2])
+        @test SparseIntSet([1, 2]) == IntSet([1, 2])
+
+        @test filter(isodd, SparseIntSet([1, 2, 3])) isa SparseIntSet
+        @test issetequal(filter(isodd, SparseIntSet([1, 2, 3])), SparseIntSet([1, 3]))
+        @test filter(_ -> false, SparseIntSet([1, 2])) isa SparseIntSet
+        @test isempty(filter(_ -> false, SparseIntSet([1, 2])))
+        @test setdiff(SparseIntSet([1, 2, 3]), [2]) isa SparseIntSet
+        @test issetequal(setdiff(SparseIntSet([1, 2, 3]), [2]), SparseIntSet([1, 3]))
+
+        s = SparseIntSet([1, 2, 3])
+        filter!(isodd, s)
+        @test issetequal(s, SparseIntSet([1, 3]))
+        @test issetequal(intersect!(SparseIntSet([1, 2, 3]), Set([2, 3, 4])), SparseIntSet([2, 3]))
+        s = SparseIntSet([1])
+        union!(s, Set([2]))
+        @test issetequal(s, SparseIntSet([1, 2]))
+
+        @test SparseIntSet([1]) == SparseIntSet([1])
+        @test SparseIntSet([1]) < SparseIntSet([1, 2])
+        @test SparseIntSet([1, 2]) <= SparseIntSet([1, 2])
+
+        # No native symdiff; AbstractSet fallback must still work
+        @test issetequal(symdiff(SparseIntSet([1, 2]), Set([2, 3])), Set([1, 3]))
+
+        @test Base.emptymutable(SparseIntSet([1])) isa SparseIntSet
+        s = SparseIntSet([1, 2])
+        cpy = Base.copymutable(s)
+        push!(cpy, 9)
+        @test 9 in cpy
+        @test !(9 in s)
+    end
+
+
 end