diff --git a/windows/exec_windows.go b/windows/exec_windows.go
index 7a11e83..855698b 100644
--- a/windows/exec_windows.go
+++ b/windows/exec_windows.go
@@ -9,8 +9,6 @@
 import (
 	errorspkg "errors"
 	"unsafe"
-
-	"golang.org/x/sys/internal/unsafeheader"
 )
 
 // EscapeArg rewrites command line argument s as prescribed
@@ -147,8 +145,12 @@
 		}
 		return nil, err
 	}
+	alloc, err := LocalAlloc(LMEM_FIXED, uint32(size))
+	if err != nil {
+		return nil, err
+	}
 	// size is guaranteed to be ≥1 by InitializeProcThreadAttributeList.
-	al := &ProcThreadAttributeListContainer{data: (*ProcThreadAttributeList)(unsafe.Pointer(&make([]byte, size)[0]))}
+	al := &ProcThreadAttributeListContainer{data: (*ProcThreadAttributeList)(unsafe.Pointer(alloc))}
 	err = initializeProcThreadAttributeList(al.data, maxAttrCount, 0, &size)
 	if err != nil {
 		return nil, err
@@ -157,36 +159,17 @@
 }
 
 // Update modifies the ProcThreadAttributeList using UpdateProcThreadAttribute.
-// Note that the value passed to this function will be copied into memory
-// allocated by LocalAlloc, the contents of which should not contain any
-// Go-managed pointers, even if the passed value itself is a Go-managed
-// pointer.
 func (al *ProcThreadAttributeListContainer) Update(attribute uintptr, value unsafe.Pointer, size uintptr) error {
-	alloc, err := LocalAlloc(LMEM_FIXED, uint32(size))
-	if err != nil {
-		return err
-	}
-	var src, dst []byte
-	hdr := (*unsafeheader.Slice)(unsafe.Pointer(&src))
-	hdr.Data = value
-	hdr.Cap = int(size)
-	hdr.Len = int(size)
-	hdr = (*unsafeheader.Slice)(unsafe.Pointer(&dst))
-	hdr.Data = unsafe.Pointer(alloc)
-	hdr.Cap = int(size)
-	hdr.Len = int(size)
-	copy(dst, src)
-	al.heapAllocations = append(al.heapAllocations, alloc)
-	return updateProcThreadAttribute(al.data, 0, attribute, unsafe.Pointer(alloc), size, nil, nil)
+	al.pointers = append(al.pointers, value)
+	return updateProcThreadAttribute(al.data, 0, attribute, value, size, nil, nil)
 }
 
 // Delete frees ProcThreadAttributeList's resources.
 func (al *ProcThreadAttributeListContainer) Delete() {
 	deleteProcThreadAttributeList(al.data)
-	for i := range al.heapAllocations {
-		LocalFree(Handle(al.heapAllocations[i]))
-	}
-	al.heapAllocations = nil
+	LocalFree(Handle(unsafe.Pointer(al.data)))
+	al.data = nil
+	al.pointers = nil
 }
 
 // List returns the actual ProcThreadAttributeList to be passed to StartupInfoEx.
diff --git a/windows/syscall_windows_test.go b/windows/syscall_windows_test.go
index 1c1a3ea..e4fe846 100644
--- a/windows/syscall_windows_test.go
+++ b/windows/syscall_windows_test.go
@@ -5,6 +5,7 @@
 package windows_test
 
 import (
+	"bufio"
 	"bytes"
 	"debug/pe"
 	"errors"
@@ -18,6 +19,7 @@
 	"strings"
 	"syscall"
 	"testing"
+	"time"
 	"unsafe"
 
 	"golang.org/x/sys/internal/unsafeheader"
@@ -1002,3 +1004,56 @@
 		t.Logf("%s - %s", drvInfoData.Description(), drvInfoDetailData.InfFileName())
 	}
 }
+
+func TestProcThreadAttributeHandleList(t *testing.T) {
+	const sentinel = "the gopher dance"
+	system32, err := windows.GetSystemDirectory()
+	if err != nil {
+		t.Fatal(err)
+	}
+	executable16, err := windows.UTF16PtrFromString(filepath.Join(system32, "cmd.exe"))
+	if err != nil {
+		t.Fatal(err)
+	}
+	args16, err := windows.UTF16PtrFromString(windows.ComposeCommandLine([]string{"/c", "echo " + sentinel}))
+	if err != nil {
+		t.Fatal(err)
+	}
+	attributeList, err := windows.NewProcThreadAttributeList(1)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer attributeList.Delete()
+	si := &windows.StartupInfoEx{
+		StartupInfo:             windows.StartupInfo{Cb: uint32(unsafe.Sizeof(windows.StartupInfoEx{}))},
+		ProcThreadAttributeList: attributeList.List(),
+	}
+	pipeR, pipeW, err := os.Pipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer pipeR.Close()
+	defer pipeW.Close()
+	func() {
+		// We allocate handles in a closure to provoke a UaF in the case of attributeList.Update being buggy.
+		handles := []windows.Handle{windows.Handle(pipeW.Fd())}
+		attributeList.Update(windows.PROC_THREAD_ATTRIBUTE_HANDLE_LIST, unsafe.Pointer(&handles[0]), uintptr(len(handles))*unsafe.Sizeof(handles[0]))
+		si.Flags |= windows.STARTF_USESTDHANDLES
+		si.StdOutput = handles[0]
+	}()
+	pi := new(windows.ProcessInformation)
+	err = windows.CreateProcess(executable16, args16, nil, nil, true, windows.CREATE_DEFAULT_ERROR_MODE|windows.CREATE_UNICODE_ENVIRONMENT|windows.EXTENDED_STARTUPINFO_PRESENT, nil, nil, &si.StartupInfo, pi)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer windows.CloseHandle(pi.Thread)
+	defer windows.CloseHandle(pi.Process)
+	pipeR.SetReadDeadline(time.Now().Add(time.Minute))
+	out, _, err := bufio.NewReader(pipeR).ReadLine()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(out) != sentinel {
+		t.Fatalf("got %q; want %q", out, sentinel)
+	}
+}
diff --git a/windows/types_windows.go b/windows/types_windows.go
index 73087bf..655447e 100644
--- a/windows/types_windows.go
+++ b/windows/types_windows.go
@@ -938,8 +938,8 @@
 type ProcThreadAttributeList struct{}
 
 type ProcThreadAttributeListContainer struct {
-	data            *ProcThreadAttributeList
-	heapAllocations []uintptr
+	data     *ProcThreadAttributeList
+	pointers []unsafe.Pointer
 }
 
 type ProcessInformation struct {