diff --git a/src/internal/poll/fd_windows.go b/src/internal/poll/fd_windows.go
index 9df39edced..2095a6aa29 100644
--- a/src/internal/poll/fd_windows.go
+++ b/src/internal/poll/fd_windows.go
@@ -1037,8 +1037,7 @@ func (fd *FD) Fchmod(mode uint32) error {
 
 	var du windows.FILE_BASIC_INFO
 	du.FileAttributes = attrs
-	l := uint32(unsafe.Sizeof(d))
-	return windows.SetFileInformationByHandle(fd.Sysfd, windows.FileBasicInfo, uintptr(unsafe.Pointer(&du)), l)
+	return windows.SetFileInformationByHandle(fd.Sysfd, windows.FileBasicInfo, unsafe.Pointer(&du), uint32(unsafe.Sizeof(du)))
 }
 
 // Fchdir wraps syscall.Fchdir.
diff --git a/src/internal/syscall/windows/syscall_windows.go b/src/internal/syscall/windows/syscall_windows.go
index 5854ca60b5..d10e30cb68 100644
--- a/src/internal/syscall/windows/syscall_windows.go
+++ b/src/internal/syscall/windows/syscall_windows.go
@@ -129,11 +129,22 @@ type SecurityAttributes struct {
 }
 
 type FILE_BASIC_INFO struct {
-	CreationTime   syscall.Filetime
-	LastAccessTime syscall.Filetime
-	LastWriteTime  syscall.Filetime
-	ChangedTime    syscall.Filetime
+	CreationTime   int64
+	LastAccessTime int64
+	LastWriteTime  int64
+	ChangedTime    int64
 	FileAttributes uint32
+
+	// Pad out to 8-byte alignment.
+	//
+	// Without this padding, TestChmod fails due to an argument validation error
+	// in SetFileInformationByHandle on windows/386.
+	//
+	// https://learn.microsoft.com/en-us/cpp/build/reference/zp-struct-member-alignment?view=msvc-170
+	// says that “The C/C++ headers in the Windows SDK assume the platform's
+	// default alignment is used.” What we see here is padding rather than
+	// alignment, but maybe it is related.
+	_ uint32
 }
 
 const (
@@ -150,7 +161,7 @@ const (
 //sys	GetComputerNameEx(nameformat uint32, buf *uint16, n *uint32) (err error) = GetComputerNameExW
 //sys	MoveFileEx(from *uint16, to *uint16, flags uint32) (err error) = MoveFileExW
 //sys	GetModuleFileName(module syscall.Handle, fn *uint16, len uint32) (n uint32, err error) = kernel32.GetModuleFileNameW
-//sys	SetFileInformationByHandle(handle syscall.Handle, fileInformationClass uint32, buf uintptr, bufsize uint32) (err error) = kernel32.SetFileInformationByHandle
+//sys	SetFileInformationByHandle(handle syscall.Handle, fileInformationClass uint32, buf unsafe.Pointer, bufsize uint32) (err error) = kernel32.SetFileInformationByHandle
 //sys	VirtualQuery(address uintptr, buffer *MemoryBasicInformation, length uintptr) (err error) = kernel32.VirtualQuery
 //sys	GetTempPath2(buflen uint32, buf *uint16) (n uint32, err error) = GetTempPath2W
 
diff --git a/src/internal/syscall/windows/zsyscall_windows.go b/src/internal/syscall/windows/zsyscall_windows.go
index 5a587ad4f1..931f157cf1 100644
--- a/src/internal/syscall/windows/zsyscall_windows.go
+++ b/src/internal/syscall/windows/zsyscall_windows.go
@@ -342,7 +342,7 @@ func RtlVirtualUnwind(handlerType uint32, baseAddress uintptr, pc uintptr, entry
 	return
 }
 
-func SetFileInformationByHandle(handle syscall.Handle, fileInformationClass uint32, buf uintptr, bufsize uint32) (err error) {
+func SetFileInformationByHandle(handle syscall.Handle, fileInformationClass uint32, buf unsafe.Pointer, bufsize uint32) (err error) {
 	r1, _, e1 := syscall.Syscall6(procSetFileInformationByHandle.Addr(), 4, uintptr(handle), uintptr(fileInformationClass), uintptr(buf), uintptr(bufsize), 0, 0)
 	if r1 == 0 {
 		err = errnoErr(e1)