diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 92fd1320..3cb18556 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -89,6 +89,36 @@ jobs:
       - uses: julia-actions/julia-uploadcodecov@latest
         env:
           CODECOV_TOKEN: ${{ secrets.CODECOV_TOKEN }}
+  test-downstream:
+    name: Julia ${{ matrix.version }} downstream - ${{ matrix.package }} [${{ matrix.env }}]
+    runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        version:
+          - '1.10'
+          - '1'
+        package:
+          - 'Mooncake'
+        env:
+          - 'old'
+          - 'new'
+    env:
+      STATICARRAYS_DOWNSTREAM_TEST_PACKAGE: ${{ matrix.package }}
+      STATICARRAYS_DOWNSTREAM_TEST_ENV: ${{ matrix.env }}
+    steps:
+      - uses: actions/checkout@v6
+      - uses: julia-actions/setup-julia@v3
+        with:
+          version: ${{ matrix.version }}
+      - uses: julia-actions/cache@v3
+      - uses: julia-actions/julia-buildpkg@v1
+      - run: julia -O1 --code-coverage=user --color=yes test/downstream/harness.jl
+      - uses: julia-actions/julia-processcoverage@v1
+      - uses: codecov/codecov-action@v6
+        with:
+          files: lcov.info
+          token: ${{ secrets.CODECOV_TOKEN }}
+          fail_ci_if_error: false
   docs:
     name: Documentation
     runs-on: ubuntu-latest
diff --git a/.gitignore b/.gitignore
index 94cabef0..d9bc4633 100644
--- a/.gitignore
+++ b/.gitignore
@@ -7,3 +7,4 @@
 /benchmark/*.json
 /benchmark/Manifest.toml
 /docs/Manifest.toml
+/test/downstream/**/Manifest.toml
\ No newline at end of file
diff --git a/Project.toml b/Project.toml
index ba8ee58d..c460612e 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,6 +1,6 @@
 name = "StaticArrays"
 uuid = "90137ffa-7385-5640-81b9-e52037218182"
-version = "1.9.18"
+version = "1.9.19"
 
 [deps]
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
@@ -11,10 +11,12 @@ Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
 [weakdeps]
 ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
+Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 
 [extensions]
 StaticArraysChainRulesCoreExt = "ChainRulesCore"
+StaticArraysMooncakeExt = "Mooncake"
 StaticArraysStatisticsExt = "Statistics"
 
 [compat]
@@ -25,6 +27,7 @@ ChainRulesTestUtils = "1"
 InteractiveUtils = "1"
 JLArrays = "0.1"
 LinearAlgebra = "1.6"
+Mooncake = "0.5"
 OffsetArrays = "1"
 PrecompileTools = "1"
 Random = "1.6"
@@ -41,6 +44,7 @@ ChainRulesCore = "d360d2e6-b24c-11e9-a2a3-2a2ae2dbcce4"
 ChainRulesTestUtils = "cdddcdb0-9152-4a09-a978-84456f9df70a"
 InteractiveUtils = "b77e0a4c-d291-57a0-90e8-8db25a27a240"
 JLArrays = "27aeb0d3-9eb9-45fb-866b-73c2ecf80fcb"
+Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
 OffsetArrays = "6fe1bfb0-de20-5000-8ca7-80f57d26f881"
 Statistics = "10745b16-79ce-11e8-11f9-7d13ad32a3b2"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
diff --git a/ext/StaticArraysMooncakeExt.jl b/ext/StaticArraysMooncakeExt.jl
new file mode 100644
index 00000000..22ede3cc
--- /dev/null
+++ b/ext/StaticArraysMooncakeExt.jl
@@ -0,0 +1,13 @@
+module StaticArraysMooncakeExt
+
+using StaticArrays: SArray,MArray
+using Mooncake: Mooncake
+
+@static if isdefined(Mooncake, :FriendlyTangentCache)  # checks Mooncake >= v0.5.25
+    # see https://github.com/JuliaDiff/DifferentiationInterface.jl/issues/998
+    function Mooncake.friendly_tangent_cache(x::Union{SArray,MArray})
+        return Mooncake.FriendlyTangentCache{Mooncake.AsPrimal}(copy(x))
+    end
+end
+
+end
diff --git a/test/downstream/Mooncake/new/Project.toml b/test/downstream/Mooncake/new/Project.toml
new file mode 100644
index 00000000..586dd7e8
--- /dev/null
+++ b/test/downstream/Mooncake/new/Project.toml
@@ -0,0 +1,10 @@
+[deps]
+Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
+StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[sources]
+StaticArrays = {path = "../../../.."}
+
+[compat]
+Mooncake = ">=0.5.25"
diff --git a/test/downstream/Mooncake/old/Project.toml b/test/downstream/Mooncake/old/Project.toml
new file mode 100644
index 00000000..5427876c
--- /dev/null
+++ b/test/downstream/Mooncake/old/Project.toml
@@ -0,0 +1,10 @@
+[deps]
+Mooncake = "da2b9cff-9c12-43a0-ae48-6db2b0edb7d6"
+StaticArrays = "90137ffa-7385-5640-81b9-e52037218182"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
+
+[sources]
+StaticArrays = {path = "../../../.."}
+
+[compat]
+Mooncake = "<0.5.25"
diff --git a/test/downstream/Mooncake/test.jl b/test/downstream/Mooncake/test.jl
new file mode 100644
index 00000000..1b0bcd9c
--- /dev/null
+++ b/test/downstream/Mooncake/test.jl
@@ -0,0 +1,20 @@
+using StaticArrays
+using Mooncake
+using Test
+
+@testset verbose=true "Mooncake integration" begin
+    f(x) = sum(abs2, x)
+    config = Mooncake.Config(; friendly_tangents=true)
+    @testset "$(typeof(x))" for x in [
+        SVector(1.0, 2.0),
+        MVector(1.0, 2.0) ,
+        SMatrix{2,2}(1.0, 2.0, 3.0, 4.0),
+        MMatrix{2,2}(1.0, 2.0, 3.0, 4.0)
+    ]
+        cache = prepare_gradient_cache(f, zero(x); config)
+        val, grads = value_and_gradient!!(cache, f, x)
+        g = grads[2]
+        @test g isa typeof(x)
+        @test g == 2x
+    end
+end
diff --git a/test/downstream/harness.jl b/test/downstream/harness.jl
new file mode 100644
index 00000000..97aaabbf
--- /dev/null
+++ b/test/downstream/harness.jl
@@ -0,0 +1,6 @@
+using Pkg
+package = ENV["STATICARRAYS_DOWNSTREAM_TEST_PACKAGE"];
+env = ENV["STATICARRAYS_DOWNSTREAM_TEST_ENV"];
+Pkg.activate(joinpath(@__DIR__, package, env))
+Pkg.develop(PackageSpec(path=joinpath(@__DIR__, "..", "..")))
+include(joinpath(package, "test.jl"))