diff --git a/test/Project.toml b/test/Project.toml
index 509e3a49f0..9974c37a38 100644
--- a/test/Project.toml
+++ b/test/Project.toml
@@ -10,6 +10,7 @@ ITensors = "9136182c-28ba-11e9-034c-db9fb085ebd5"
 JLD2 = "033835bb-8acc-5ee8-8aae-3f567f8a3819"
 KrylovKit = "0b1a1467-8014-51b9-945f-bf0ae24f4b77"
 LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
+MappedArrays = "dbb5928d-eab1-5f90-85c2-b9b0edb7c900"
 NDTensors = "23ae76d9-e61a-49c4-8f12-3f1a16adf9cf"
 OptimKit = "77e91f04-9b3b-57a6-a776-40b61faaebe0"
 PackageCompiler = "9b87118b-4619-50d2-8e1e-99f35a4d4d9d"
diff --git a/test/ext/NDTensorsMappedArraysExt/Project.toml b/test/ext/NDTensorsMappedArraysExt/Project.toml
new file mode 100644
index 0000000000..2236ea0414
--- /dev/null
+++ b/test/ext/NDTensorsMappedArraysExt/Project.toml
@@ -0,0 +1,5 @@
+[deps]
+ITensors = "9136182c-28ba-11e9-034c-db9fb085ebd5"
+LinearAlgebra = "37e2e46d-f89d-539d-b4ee-838fcccc9c8e"
+MappedArrays = "dbb5928d-eab1-5f90-85c2-b9b0edb7c900"
+Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
diff --git a/test/ext/NDTensorsMappedArraysExt/runtests.jl b/test/ext/NDTensorsMappedArraysExt/runtests.jl
new file mode 100644
index 0000000000..6c38ed96fa
--- /dev/null
+++ b/test/ext/NDTensorsMappedArraysExt/runtests.jl
@@ -0,0 +1,24 @@
+@eval module $(gensym())
+using ITensors: Index, itensor
+using LinearAlgebra: qr, svd
+using MappedArrays: mappedarray
+using Test: @test, @testset
+f(i::Int...) = float(sum(iⱼ -> iⱼ^2, i))
+f(i::CartesianIndex) = f(Tuple(i)...)
+@testset "NDTensorsMappedArraysExt" begin
+  a = mappedarray(f, CartesianIndices((2, 2)))
+  b = copy(a)
+  i, j = Index.((2, 2))
+  ta = itensor(a, i, j)
+  tb = itensor(b, i, j)
+  @test ta ≈ tb
+  @test ta[i => 1, j => 2] ≈ tb[i => 1, j => 2]
+  @test 2 * ta ≈ 2 * tb
+  @test ta + ta ≈ tb + tb
+  @test ta * ta ≈ tb * tb
+  ua, sa, va = svd(ta, i)
+  @test ua * sa * va ≈ ta
+  qa, ra = qr(ta, i)
+  @test qa * ra ≈ ta
+end
+end
diff --git a/test/runtests.jl b/test/runtests.jl
index 88af73a005..a0c92a13a1 100644
--- a/test/runtests.jl
+++ b/test/runtests.jl
@@ -22,6 +22,7 @@ ITensors.disable_threaded_blocksparse()
       "ext/ITensorsChainRulesCoreExt",
       "ext/ITensorsPackageCompilerExt",
       "ext/ITensorsVectorInterfaceExt",
+      "ext/NDTensorsMappedArraysExt",
     ]
     @time for dir in dirs
       println("\nTest $(@__DIR__)/$(dir)")