diff --git a/stdlib/LinearAlgebra/src/lu.jl b/stdlib/LinearAlgebra/src/lu.jl
index 68c085a68b47a..48a167356e91e 100644
--- a/stdlib/LinearAlgebra/src/lu.jl
+++ b/stdlib/LinearAlgebra/src/lu.jl
@@ -496,7 +496,8 @@ factorize(A::Tridiagonal) = lu(A)
 function getproperty(F::LU{T,Tridiagonal{T,V}}, d::Symbol) where {T,V}
     m, n = size(F)
     if d == :L
-        L = Array(Bidiagonal(fill(one(T), n), getfield(getfield(F, :factors), :dl), d))
+        dl = getfield(getfield(F, :factors), :dl)
+        L = Array(Bidiagonal(fill!(similar(dl, n), one(T)), dl, d))
         for i = 2:n
             tmp = L[getfield(F, :ipiv)[i], 1:i - 1]
             L[getfield(F, :ipiv)[i], 1:i - 1] = L[i, 1:i - 1]
diff --git a/stdlib/LinearAlgebra/test/tridiag.jl b/stdlib/LinearAlgebra/test/tridiag.jl
index 88f28a02456d6..dcde93b03c1a1 100644
--- a/stdlib/LinearAlgebra/test/tridiag.jl
+++ b/stdlib/LinearAlgebra/test/tridiag.jl
@@ -384,4 +384,11 @@ end
     @test SymTridiagonal(ones(0), ones(0)) * ones(0, 2) == ones(0, 2)
 end
 
+@testset "issue #29644" begin
+    F = lu(Tridiagonal(sparse(1.0I, 3, 3)))
+    @test F.L == Matrix(I, 3, 3)
+    @test startswith(sprint(show, MIME("text/plain"), F),
+          "LinearAlgebra.LU{Float64,LinearAlgebra.Tridiagonal{Float64,SparseArrays.SparseVector")
+end
+
 end # module TestTridiagonal