diff --git a/base/sort.jl b/base/sort.jl
index b78f773ad9f72..99f2ed3e1aeb8 100644
--- a/base/sort.jl
+++ b/base/sort.jl
@@ -1809,7 +1809,7 @@ function sort!(A::AbstractArray{T};
                by=identity,
                rev::Union{Bool,Nothing}=nothing,
                order::Ordering=Forward, # TODO stop eagerly over-allocating.
-               scratch::Union{Vector{T}, Nothing}=similar(A, size(A, dims))) where T
+               scratch::Union{Vector{T}, Nothing}=Vector{T}(undef, size(A, dims))) where T
     __sort!(A, Val(dims), maybe_apply_initial_optimizations(alg), ord(lt, by, rev, order), scratch)
 end
 function __sort!(A::AbstractArray{T}, ::Val{K},
diff --git a/test/sorting.jl b/test/sorting.jl
index 0528d9d81c296..cf98182307088 100644
--- a/test/sorting.jl
+++ b/test/sorting.jl
@@ -1011,6 +1011,20 @@ end
     end
 end
 
+struct MyArray49392{T, N} <: AbstractArray{T, N}
+    data::Array{T, N}
+end
+Base.size(A::MyArray49392) = size(A.data)
+Base.getindex(A::MyArray49392, i...) = getindex(A.data, i...)
+Base.setindex!(A::MyArray49392, v, i...) = setindex!(A.data, v, i...)
+Base.similar(A::MyArray49392, ::Type{T}, dims::Dims{N}) where {T, N} = MyArray49392(similar(A.data, T, dims))
+
+@testset "Custom matrices (#49392)" begin
+    x = rand(10, 10)
+    y = MyArray49392(copy(x))
+    @test all(sort!(y, dims=2) .== sort!(x,dims=2))
+end
+
 # This testset is at the end of the file because it is slow.
 @testset "searchsorted" begin
     numTypes = [ Int8,  Int16,  Int32,  Int64,  Int128,