diff --git a/Project.toml b/Project.toml
index 34a16ea..541cf5e 100644
--- a/Project.toml
+++ b/Project.toml
@@ -12,10 +12,11 @@ ArgTools = "1.1"
 julia = "1.3"
 
 [extras]
+Pkg = "44cfe95a-1eb2-52ea-b672-e2afdf69b78f"
 Random = "9a3f8284-a2c9-5f02-9a11-845980a1fd5c"
 SimpleBufferStream = "777ac1f9-54b0-4bf8-805c-2214025038e7"
 Tar_jll = "9b64493d-8859-5bf3-93d7-7c32dd38186f"
 Test = "8dfed614-e22c-5e08-85e1-65c5234f0b40"
 
 [targets]
-test = ["Random", "Tar_jll", "Test", "SimpleBufferStream"]
+test = ["Pkg", "Random", "Tar_jll", "Test", "SimpleBufferStream"]
diff --git a/src/extract.jl b/src/extract.jl
index 6da350e..877d42d 100644
--- a/src/extract.jl
+++ b/src/extract.jl
@@ -73,18 +73,12 @@ function extract_tarball(
             copy_symlinks || symlink(hdr.link, sys_path)
         elseif hdr.type == :file
             read_data(tar, sys_path, size=hdr.size, buf=buf)
-            # change executable bit if necessary
-            if Sys.iswindows() ⊻ !iszero(0o100 & hdr.mode)
+            # set executable bit if necessary
+            if !iszero(hdr.mode & 0o100)
                 mode = filemode(sys_path)
-                if Sys.iswindows()
-                    # turn off all execute bits
-                    mode &= 0o666
-                else
-                    # copy read bits to execute bits with
-                    # at least the user execute bit on
-                    mode |= 0o100 | (mode & 0o444) >> 2
-                end
-                chmod(sys_path, mode)
+                # exec bits = read bits, but set user read at least:
+                chmod(sys_path, mode | ((mode & 0o444) >> 2) | 0o100)
+                # TODO: use actual umask exec bits instead?
             end
         else # should already be caught by check_header
             error("unsupported tarball entry type: $(hdr.type)")
@@ -132,19 +126,6 @@ function extract_tarball(
                 src = reduce(joinpath, init=root, split(what, '/'))
                 dst = reduce(joinpath, init=root, split(path, '/'))
                 cp(src, dst)
-                if Sys.iswindows()
-                    # our `cp` doesn't copy ACL properties, so manually set them via `chmod`
-                    function copy_mode(src::String, dst::String)
-                        chmod(dst, filemode(src))
-                        isdir(dst) || return
-                        for name in readdir(dst)
-                            sub_src = joinpath(src, name)
-                            sub_dst = joinpath(dst, name)
-                            copy_mode(sub_src, sub_dst)
-                        end
-                    end
-                    copy_mode(src, dst)
-                end
             end
         end
     end
diff --git a/src/header.jl b/src/header.jl
index 3df7135..8e3d2c9 100644
--- a/src/header.jl
+++ b/src/header.jl
@@ -132,13 +132,7 @@ function path_header(sys_path::AbstractString, tar_path::AbstractString)
     elseif isfile(st)
         size = filesize(st)
         type = :file
-        # Windows can't re-use the `lstat` result, we need to ask
-        # the system whether it's executable or not via `access()`
-        if Sys.iswindows()
-            mode = Sys.isexecutable(sys_path) ? 0o755 : 0o644
-        else
-            mode = iszero(filemode(st) & 0o100) ? 0o644 : 0o755
-        end
+        mode = iszero(filemode(st) & 0o100) ? 0o644 : 0o755
         link = ""
     else
         error("unsupported file type: $(repr(sys_path))")
diff --git a/test/git_tools.jl b/test/git_tools.jl
deleted file mode 100644
index dd09902..0000000
--- a/test/git_tools.jl
+++ /dev/null
@@ -1,130 +0,0 @@
-# copied from Pkg.jl/src/GitTools.jl
-
-module GitTools
-
-using SHA
-import Base: SHA1
-
-@enum GitMode mode_dir=0o040000 mode_normal=0o100644 mode_executable=0o100755 mode_symlink=0o120000 mode_submodule=0o160000
-Base.string(mode::GitMode) = string(UInt32(mode); base=8)
-Base.print(io::IO, mode::GitMode) = print(io, string(mode))
-
-function gitmode(path::AbstractString)
-    if islink(path)
-        return mode_symlink
-    elseif isdir(path)
-        return mode_dir
-    elseif Sys.isexecutable(path)
-        return mode_executable
-    else
-        return mode_normal
-    end
-end
-
-"""
-    blob_hash(HashType::Type, path::AbstractString)
-
-Calculate the git blob hash of a given path.
-"""
-function blob_hash(::Type{HashType}, path::AbstractString) where HashType
-    ctx = HashType()
-    if islink(path)
-        datalen = length(readlink(path))
-    else
-        datalen = filesize(path)
-    end
-
-    # First, the header
-    SHA.update!(ctx, Vector{UInt8}("blob $(datalen)\0"))
-
-    # Next, read data in in chunks of 4KB
-    buff = Vector{UInt8}(undef, 4*1024)
-
-    try
-        if islink(path)
-            update!(ctx, Vector{UInt8}(readlink(path)))
-        else
-            open(path, "r") do io
-                while !eof(io)
-                    num_read = readbytes!(io, buff)
-                    update!(ctx, buff, num_read)
-                end
-            end
-        end
-    catch e
-        if isa(e, InterruptException)
-            rethrow(e)
-        end
-        @warn("Unable to open $(path) for hashing; git-tree-sha1 likely suspect")
-    end
-
-    # Finish it off and return the digest!
-    return SHA.digest!(ctx)
-end
-blob_hash(path::AbstractString) = blob_hash(SHA1_CTX, path)
-
-"""
-    contains_files(root::AbstractString)
-
-Helper function to determine whether a directory contains files; e.g. it is a
-direct parent of a file or it contains some other directory that itself is a
-direct parent of a file. This is used to exclude directories from tree hashing.
-"""
-function contains_files(path::AbstractString)
-    st = lstat(path)
-    ispath(st) || throw(ArgumentError("non-existent path: $(repr(path))"))
-    isdir(st) || return true
-    for p in readdir(path)
-        contains_files(joinpath(path, p)) && return true
-    end
-    return false
-end
-
-
-"""
-    tree_hash(HashType::Type, root::AbstractString)
-
-Calculate the git tree hash of a given path.
-"""
-function tree_hash(::Type{HashType}, root::AbstractString) where HashType
-    entries = Tuple{String, Vector{UInt8}, GitMode}[]
-    for f in readdir(root)
-        # Skip `.git` directories
-        if f == ".git"
-            continue
-        end
-
-        filepath = abspath(root, f)
-        mode = gitmode(filepath)
-        if mode == mode_dir
-            # If this directory contains no files, then skip it
-            contains_files(filepath) || continue
-
-            # Otherwise, hash it up!
-            hash = tree_hash(HashType, filepath)
-        else
-            hash = blob_hash(HashType, filepath)
-        end
-        push!(entries, (f, hash, mode))
-    end
-
-    # Sort entries by name (with trailing slashes for directories)
-    sort!(entries, by = ((name, hash, mode),) -> mode == mode_dir ? name*"/" : name)
-
-    content_size = 0
-    for (n, h, m) in entries
-        content_size += ndigits(UInt32(m); base=8) + 1 + sizeof(n) + 1 + sizeof(h)
-    end
-
-    # Return the hash of these entries
-    ctx = HashType()
-    SHA.update!(ctx, Vector{UInt8}("tree $(content_size)\0"))
-    for (name, hash, mode) in entries
-        SHA.update!(ctx, Vector{UInt8}("$(mode) $(name)\0"))
-        SHA.update!(ctx, hash)
-    end
-    return SHA.digest!(ctx)
-end
-tree_hash(root::AbstractString) = tree_hash(SHA.SHA1_CTX, root)
-
-end # module
diff --git a/test/setup.jl b/test/setup.jl
index 5d2f4e9..31b9153 100644
--- a/test/setup.jl
+++ b/test/setup.jl
@@ -3,8 +3,7 @@ using Random
 using ArgTools
 
 import Tar
-
-include("git_tools.jl")
+import Pkg.GitTools
 
 const NON_STDLIB_TESTS = Main == @__MODULE__