diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 38db71eb..65171ce2 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -17,7 +17,7 @@ jobs:
         version:
           - 'lts' # Replace this with the minimum Julia version that your package supports. E.g. if your package requires Julia 1.5 or higher, change this to '1.5'.
           - '1'   # Leave this line unchanged. '1' will automatically expand to the latest stable 1.x release of Julia.
-          - 'nightly'
+          - 'pre'
         os:
           - ubuntu-latest
           - windows-latest
diff --git a/Project.toml b/Project.toml
index 75b13fb8..4191d334 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "ExtendableGrids"
 uuid = "cfc395e8-590f-11e8-1f13-43a2532b2fa8"
 authors = ["Juergen Fuhrmann <juergen.fuhrmann@wias-berlin.de>", "Christian Merdon  <christian.merdon@wias-berlin.de>", "Johannes Taraz  <johannes.taraz@gmail.com>", "Patrick Jaap <patrick.jaap@wias-berlin.de>"]
-version = "1.13"
+version = "1.13.1"
 
 [deps]
 AbstractTrees = "1520ce14-60c1-5f80-bbc7-55ef81b5835c"
diff --git a/src/adjacency.jl b/src/adjacency.jl
index fb53d2ad..63e4e67e 100644
--- a/src/adjacency.jl
+++ b/src/adjacency.jl
@@ -109,7 +109,7 @@ max_num_targets_per_source(adj::VariableTargetAdjacency) = maximum(adj.colstart[
 Base.size(adj::VariableTargetAdjacency) = (max_num_targets_per_source(adj), num_sources(adj))
 
 
-function Matrix(adj::VariableTargetAdjacency{T}) where {T}
+function Base.Matrix(adj::VariableTargetAdjacency{T}) where {T}
     m = zeros(T, size(adj)...)
     for isrc in 1:num_sources(adj)
         for itgt in 1:num_targets(adj, isrc)
diff --git a/src/io.jl b/src/io.jl
index fe17c2d5..553aa026 100644
--- a/src/io.jl
+++ b/src/io.jl
@@ -1,11 +1,11 @@
 using WriteVTK
 
 # conversion from AbstractElementGeometry to WriteVTK.VTKCellTypes
-VTKCellType(::Type{<:AbstractElementGeometry1D}) = VTKCellTypes.VTK_LINE
-VTKCellType(::Type{<:Triangle2D}) = VTKCellTypes.VTK_TRIANGLE
-VTKCellType(::Type{<:Quadrilateral2D}) = VTKCellTypes.VTK_QUAD
-VTKCellType(::Type{<:Tetrahedron3D}) = VTKCellTypes.VTK_TETRA
-VTKCellType(::Type{<:Hexahedron3D}) = VTKCellTypes.VTK_HEXAHEDRON
+WriteVTK.VTKCellType(::Type{<:AbstractElementGeometry1D}) = VTKCellTypes.VTK_LINE
+WriteVTK.VTKCellType(::Type{<:Triangle2D}) = VTKCellTypes.VTK_TRIANGLE
+WriteVTK.VTKCellType(::Type{<:Quadrilateral2D}) = VTKCellTypes.VTK_QUAD
+WriteVTK.VTKCellType(::Type{<:Tetrahedron3D}) = VTKCellTypes.VTK_TETRA
+WriteVTK.VTKCellType(::Type{<:Hexahedron3D}) = VTKCellTypes.VTK_HEXAHEDRON
 
 """
 $(TYPEDSIGNATURES)