diff --git a/src/runtime/cgocall.go b/src/runtime/cgocall.go
index 05fa47158a..e81852f607 100644
--- a/src/runtime/cgocall.go
+++ b/src/runtime/cgocall.go
@@ -181,8 +181,14 @@ func cgocall(fn, arg unsafe.Pointer) int32 {
 
 	osPreemptExtExit(mp)
 
+	// Save current syscall parameters, so m.winsyscall can be
+	// used again if callback decide to make syscall.
+	winsyscall := mp.winsyscall
+
 	exitsyscall()
 
+	getg().m.winsyscall = winsyscall
+
 	// Note that raceacquire must be called only after exitsyscall has
 	// wired this M to a P.
 	if raceenabled {
@@ -297,9 +303,9 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 
 	checkm := gp.m
 
-	// Save current syscall parameters, so m.syscall can be
+	// Save current syscall parameters, so m.winsyscall can be
 	// used again if callback decide to make syscall.
-	syscall := gp.m.syscall
+	winsyscall := gp.m.winsyscall
 
 	// entersyscall saves the caller's SP to allow the GC to trace the Go
 	// stack. However, since we're returning to an earlier stack frame and
@@ -340,7 +346,7 @@ func cgocallbackg(fn, frame unsafe.Pointer, ctxt uintptr) {
 	// going back to cgo call
 	reentersyscall(savedpc, uintptr(savedsp))
 
-	gp.m.syscall = syscall
+	gp.m.winsyscall = winsyscall
 }
 
 func cgocallbackg1(fn, frame unsafe.Pointer, ctxt uintptr) {
diff --git a/src/runtime/nonwindows_stub.go b/src/runtime/nonwindows_stub.go
index e420acf185..859ae48004 100644
--- a/src/runtime/nonwindows_stub.go
+++ b/src/runtime/nonwindows_stub.go
@@ -21,3 +21,8 @@ func osRelax(relax bool) {}
 // enableWER is called by setTraceback("wer").
 // Windows Error Reporting (WER) is only supported on Windows.
 func enableWER() {}
+
+// winlibcall is not implemented on non-Windows systems,
+// but it is used in non-OS-specific parts of the runtime.
+// Define it as an empty struct to avoid wasting stack space.
+type winlibcall struct{}
diff --git a/src/runtime/os_windows.go b/src/runtime/os_windows.go
index 0074b9358a..d65e0c91f4 100644
--- a/src/runtime/os_windows.go
+++ b/src/runtime/os_windows.go
@@ -214,6 +214,8 @@ func asmstdcall(fn unsafe.Pointer)
 
 var asmstdcallAddr unsafe.Pointer
 
+type winlibcall libcall
+
 func windowsFindfunc(lib uintptr, name []byte) stdFunction {
 	if name[len(name)-1] != 0 {
 		throw("usage")
diff --git a/src/runtime/runtime2.go b/src/runtime/runtime2.go
index 4a7ad27172..c335f8c9d0 100644
--- a/src/runtime/runtime2.go
+++ b/src/runtime/runtime2.go
@@ -612,11 +612,11 @@ type m struct {
 
 	// these are here because they are too large to be on the stack
 	// of low-level NOSPLIT functions.
-	libcall   libcall
-	libcallpc uintptr // for cpu profiler
-	libcallsp uintptr
-	libcallg  guintptr
-	syscall   libcall // stores syscall parameters on windows
+	libcall    libcall
+	libcallpc  uintptr // for cpu profiler
+	libcallsp  uintptr
+	libcallg   guintptr
+	winsyscall winlibcall // stores syscall parameters on windows
 
 	vdsoSP uintptr // SP for traceback while in VDSO call (0 if not in call)
 	vdsoPC uintptr // PC for traceback while in VDSO call
diff --git a/src/runtime/syscall_windows.go b/src/runtime/syscall_windows.go
index 0b08583563..09762aed51 100644
--- a/src/runtime/syscall_windows.go
+++ b/src/runtime/syscall_windows.go
@@ -500,16 +500,18 @@ func syscall_SyscallN(fn uintptr, args ...uintptr) (r1, r2, err uintptr) {
 	}
 
 	// The cgocall parameters are stored in m instead of in
-	// the stack because the stack can move during if fn
+	// the stack because the stack can move during fn if it
 	// calls back into Go.
-	lockOSThread()
-	defer unlockOSThread()
-	c := &getg().m.syscall
+	c := &getg().m.winsyscall
 	c.fn = fn
 	c.n = uintptr(len(args))
 	if c.n != 0 {
 		c.args = uintptr(noescape(unsafe.Pointer(&args[0])))
 	}
 	cgocall(asmstdcallAddr, unsafe.Pointer(c))
+	// cgocall may reschedule us on to a different M,
+	// but it copies the return values into the new M's
+	// so we can read them from there.
+	c = &getg().m.winsyscall
 	return c.r1, c.r2, c.err
 }