diff --git a/windows/syscall_windows.go b/windows/syscall_windows.go
index 39e3b386..9c28e8ad 100644
--- a/windows/syscall_windows.go
+++ b/windows/syscall_windows.go
@@ -263,7 +263,7 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	GetLongPathName(path *uint16, buf *uint16, buflen uint32) (n uint32, err error) = kernel32.GetLongPathNameW
 //sys	GetShortPathName(longpath *uint16, shortpath *uint16, buflen uint32) (n uint32, err error) = kernel32.GetShortPathNameW
 //sys	GetFinalPathNameByHandle(file Handle, filePath *uint16, filePathSize uint32, flags uint32) (n uint32, err error) = kernel32.GetFinalPathNameByHandleW
-//sys	CreateFileMapping(fhandle Handle, sa *SecurityAttributes, prot uint32, maxSizeHigh uint32, maxSizeLow uint32, name *uint16) (handle Handle, err error) = kernel32.CreateFileMappingW
+//sys	CreateFileMapping(fhandle Handle, sa *SecurityAttributes, prot uint32, maxSizeHigh uint32, maxSizeLow uint32, name *uint16) (handle Handle, err error) [failretval == 0 || e1 == ERROR_ALREADY_EXISTS] = kernel32.CreateFileMappingW
 //sys	MapViewOfFile(handle Handle, access uint32, offsetHigh uint32, offsetLow uint32, length uintptr) (addr uintptr, err error)
 //sys	UnmapViewOfFile(addr uintptr) (err error)
 //sys	FlushViewOfFile(addr uintptr, length uintptr) (err error)
@@ -324,14 +324,14 @@ func NewCallbackCDecl(fn interface{}) uintptr {
 //sys	CreateSymbolicLink(symlinkfilename *uint16, targetfilename *uint16, flags uint32) (err error) [failretval&0xff==0] = CreateSymbolicLinkW
 //sys	CreateHardLink(filename *uint16, existingfilename *uint16, reserved uintptr) (err error) [failretval&0xff==0] = CreateHardLinkW
 //sys	GetCurrentThreadId() (id uint32)
-//sys	CreateEvent(eventAttrs *SecurityAttributes, manualReset uint32, initialState uint32, name *uint16) (handle Handle, err error) = kernel32.CreateEventW
-//sys	CreateEventEx(eventAttrs *SecurityAttributes, name *uint16, flags uint32, desiredAccess uint32) (handle Handle, err error) = kernel32.CreateEventExW
+//sys	CreateEvent(eventAttrs *SecurityAttributes, manualReset uint32, initialState uint32, name *uint16) (handle Handle, err error) [failretval == 0 || e1 == ERROR_ALREADY_EXISTS] = kernel32.CreateEventW
+//sys	CreateEventEx(eventAttrs *SecurityAttributes, name *uint16, flags uint32, desiredAccess uint32) (handle Handle, err error) [failretval == 0 || e1 == ERROR_ALREADY_EXISTS] = kernel32.CreateEventExW
 //sys	OpenEvent(desiredAccess uint32, inheritHandle bool, name *uint16) (handle Handle, err error) = kernel32.OpenEventW
 //sys	SetEvent(event Handle) (err error) = kernel32.SetEvent
 //sys	ResetEvent(event Handle) (err error) = kernel32.ResetEvent
 //sys	PulseEvent(event Handle) (err error) = kernel32.PulseEvent
-//sys	CreateMutex(mutexAttrs *SecurityAttributes, initialOwner bool, name *uint16) (handle Handle, err error) = kernel32.CreateMutexW
-//sys	CreateMutexEx(mutexAttrs *SecurityAttributes, name *uint16, flags uint32, desiredAccess uint32) (handle Handle, err error) = kernel32.CreateMutexExW
+//sys	CreateMutex(mutexAttrs *SecurityAttributes, initialOwner bool, name *uint16) (handle Handle, err error) [failretval == 0 || e1 == ERROR_ALREADY_EXISTS] = kernel32.CreateMutexW
+//sys	CreateMutexEx(mutexAttrs *SecurityAttributes, name *uint16, flags uint32, desiredAccess uint32) (handle Handle, err error) [failretval == 0 || e1 == ERROR_ALREADY_EXISTS] = kernel32.CreateMutexExW
 //sys	OpenMutex(desiredAccess uint32, inheritHandle bool, name *uint16) (handle Handle, err error) = kernel32.OpenMutexW
 //sys	ReleaseMutex(mutex Handle) (err error) = kernel32.ReleaseMutex
 //sys	SleepEx(milliseconds uint32, alertable bool) (ret uint32) = kernel32.SleepEx
diff --git a/windows/zsyscall_windows.go b/windows/zsyscall_windows.go
index 4e463c07..e5b190ed 100644
--- a/windows/zsyscall_windows.go
+++ b/windows/zsyscall_windows.go
@@ -1478,7 +1478,7 @@ func CreateDirectory(path *uint16, sa *SecurityAttributes) (err error) {
 func CreateEventEx(eventAttrs *SecurityAttributes, name *uint16, flags uint32, desiredAccess uint32) (handle Handle, err error) {
 	r0, _, e1 := syscall.Syscall6(procCreateEventExW.Addr(), 4, uintptr(unsafe.Pointer(eventAttrs)), uintptr(unsafe.Pointer(name)), uintptr(flags), uintptr(desiredAccess), 0, 0)
 	handle = Handle(r0)
-	if handle == 0 {
+	if handle == 0 || e1 == ERROR_ALREADY_EXISTS {
 		err = errnoErr(e1)
 	}
 	return
@@ -1487,7 +1487,7 @@ func CreateEventEx(eventAttrs *SecurityAttributes, name *uint16, flags uint32, d
 func CreateEvent(eventAttrs *SecurityAttributes, manualReset uint32, initialState uint32, name *uint16) (handle Handle, err error) {
 	r0, _, e1 := syscall.Syscall6(procCreateEventW.Addr(), 4, uintptr(unsafe.Pointer(eventAttrs)), uintptr(manualReset), uintptr(initialState), uintptr(unsafe.Pointer(name)), 0, 0)
 	handle = Handle(r0)
-	if handle == 0 {
+	if handle == 0 || e1 == ERROR_ALREADY_EXISTS {
 		err = errnoErr(e1)
 	}
 	return
@@ -1496,7 +1496,7 @@ func CreateEvent(eventAttrs *SecurityAttributes, manualReset uint32, initialStat
 func CreateFileMapping(fhandle Handle, sa *SecurityAttributes, prot uint32, maxSizeHigh uint32, maxSizeLow uint32, name *uint16) (handle Handle, err error) {
 	r0, _, e1 := syscall.Syscall6(procCreateFileMappingW.Addr(), 6, uintptr(fhandle), uintptr(unsafe.Pointer(sa)), uintptr(prot), uintptr(maxSizeHigh), uintptr(maxSizeLow), uintptr(unsafe.Pointer(name)))
 	handle = Handle(r0)
-	if handle == 0 {
+	if handle == 0 || e1 == ERROR_ALREADY_EXISTS {
 		err = errnoErr(e1)
 	}
 	return
@@ -1540,7 +1540,7 @@ func CreateJobObject(jobAttr *SecurityAttributes, name *uint16) (handle Handle,
 func CreateMutexEx(mutexAttrs *SecurityAttributes, name *uint16, flags uint32, desiredAccess uint32) (handle Handle, err error) {
 	r0, _, e1 := syscall.Syscall6(procCreateMutexExW.Addr(), 4, uintptr(unsafe.Pointer(mutexAttrs)), uintptr(unsafe.Pointer(name)), uintptr(flags), uintptr(desiredAccess), 0, 0)
 	handle = Handle(r0)
-	if handle == 0 {
+	if handle == 0 || e1 == ERROR_ALREADY_EXISTS {
 		err = errnoErr(e1)
 	}
 	return
@@ -1553,7 +1553,7 @@ func CreateMutex(mutexAttrs *SecurityAttributes, initialOwner bool, name *uint16
 	}
 	r0, _, e1 := syscall.Syscall(procCreateMutexW.Addr(), 3, uintptr(unsafe.Pointer(mutexAttrs)), uintptr(_p0), uintptr(unsafe.Pointer(name)))
 	handle = Handle(r0)
-	if handle == 0 {
+	if handle == 0 || e1 == ERROR_ALREADY_EXISTS {
 		err = errnoErr(e1)
 	}
 	return