diff --git a/app/internal/windows/windows.go b/app/internal/windows/windows.go
index 517dec45..65a01d3f 100644
--- a/app/internal/windows/windows.go
+++ b/app/internal/windows/windows.go
@@ -679,6 +679,10 @@ func UpdateWindow(hwnd syscall.Handle) {
 	_UpdateWindow.Call(uintptr(hwnd))
 }
 
+func (p WindowPlacement) Rect() Rect {
+	return p.rcNormalPosition
+}
+
 // issue34474KeepAlive calls runtime.KeepAlive as a
 // workaround for golang.org/issue/34474.
 func issue34474KeepAlive(v interface{}) {
diff --git a/app/os_macos.go b/app/os_macos.go
index be511998..270db6a6 100644
--- a/app/os_macos.go
+++ b/app/os_macos.go
@@ -97,6 +97,11 @@ static void toggleFullScreen(CFTypeRef windowRef) {
 	[window toggleFullScreen:nil];
 }
 
+static NSWindowStyleMask getWindowStyleMask(CFTypeRef windowRef) {
+	NSWindow *window = (__bridge NSWindow *)windowRef;
+	return [window styleMask];
+}
+
 static void closeWindow(CFTypeRef windowRef) {
 	NSWindow* window = (__bridge NSWindow *)windowRef;
 	[window performClose:nil];
@@ -227,10 +232,20 @@ func (w *window) WriteClipboard(s string) {
 	C.writeClipboard(chars, C.NSUInteger(len(u16)))
 }
 
+func (w *window) updateWindowMode() {
+	style := int(C.getWindowStyleMask(w.window))
+	if style&C.NSWindowStyleMaskFullScreen > 0 {
+		w.config.Mode = Fullscreen
+	} else {
+		w.config.Mode = Windowed
+	}
+}
+
 func (w *window) Configure(options []Option) {
 	screenScale := float32(C.getScreenBackingScale())
 	cfg := configFor(screenScale)
 	prev := w.config
+	w.updateWindowMode()
 	cnf := w.config
 	cnf.apply(cfg, options)
 	cnf.Size = cnf.Size.Div(int(screenScale))
@@ -473,6 +488,20 @@ func gio_onShow(view C.CFTypeRef) {
 	w.setStage(system.StageRunning)
 }
 
+//export gio_onFullscreen
+func gio_onFullscreen(view C.CFTypeRef) {
+	w := mustView(view)
+	w.config.Mode = Fullscreen
+	w.w.Event(ConfigEvent{Config: w.config})
+}
+
+//export gio_onWindowed
+func gio_onWindowed(view C.CFTypeRef) {
+	w := mustView(view)
+	w.config.Mode = Windowed
+	w.w.Event(ConfigEvent{Config: w.config})
+}
+
 //export gio_onAppHide
 func gio_onAppHide() {
 	for _, w := range viewMap {
diff --git a/app/os_macos.m b/app/os_macos.m
index 7ec868bb..f65099b7 100644
--- a/app/os_macos.m
+++ b/app/os_macos.m
@@ -23,6 +23,14 @@ __attribute__ ((visibility ("hidden"))) CALayer *gio_layerFactory(void);
 	NSWindow *window = (NSWindow *)[notification object];
 	gio_onShow((__bridge CFTypeRef)window.contentView);
 }
+- (void)windowWillEnterFullScreen:(NSNotification *)notification {
+	NSWindow *window = (NSWindow *)[notification object];
+	gio_onFullscreen((__bridge CFTypeRef)window.contentView);
+}
+- (void)windowWillExitFullScreen:(NSNotification *)notification {
+	NSWindow *window = (NSWindow *)[notification object];
+	gio_onWindowed((__bridge CFTypeRef)window.contentView);
+}
 - (void)windowDidChangeScreen:(NSNotification *)notification {
 	NSWindow *window = (NSWindow *)[notification object];
 	CGDirectDisplayID dispID = [[[window screen] deviceDescription][@"NSScreenNumber"] unsignedIntValue];
diff --git a/app/os_windows.go b/app/os_windows.go
index ed3ad447..ecbffb4d 100644
--- a/app/os_windows.go
+++ b/app/os_windows.go
@@ -282,6 +282,27 @@ func windowProc(hwnd syscall.Handle, msg uint32, wParam, lParam uintptr) uintptr
 		case windows.SIZE_MINIMIZED:
 			w.setStage(system.StagePaused)
 		case windows.SIZE_MAXIMIZED, windows.SIZE_RESTORED:
+			var triggerEvent bool
+			// Check the window size change.
+			var r windows.Rect
+			windows.GetClientRect(w.hwnd, &r)
+			size := image.Point{
+				X: int(r.Right - r.Left),
+				Y: int(r.Bottom - r.Top),
+			}
+			if size != w.config.Size {
+				w.config.Size = size
+				triggerEvent = true
+			}
+			// Check the window mode.
+			mode := w.config.Mode
+			w.updateWindowMode()
+			if mode != w.config.Mode {
+				triggerEvent = true
+			}
+			if triggerEvent {
+				w.w.Event(ConfigEvent{Config: w.config})
+			}
 			w.setStage(system.StageRunning)
 		}
 	case windows.WM_GETMINMAXINFO:
@@ -426,16 +447,6 @@ func (w *window) setStage(s system.Stage) {
 }
 
 func (w *window) draw(sync bool) {
-	var r windows.Rect
-	windows.GetClientRect(w.hwnd, &r)
-	size := image.Point{
-		X: int(r.Right - r.Left),
-		Y: int(r.Bottom - r.Top),
-	}
-	if size != w.config.Size {
-		w.config.Size = size
-		w.w.Event(ConfigEvent{Config: w.config})
-	}
 	if w.config.Size.X == 0 || w.config.Size.Y == 0 {
 		return
 	}
@@ -492,10 +503,22 @@ func (w *window) readClipboard() error {
 	return nil
 }
 
+func (w *window) updateWindowMode() {
+	p := windows.GetWindowPlacement(w.hwnd)
+	r := p.Rect()
+	mi := windows.GetMonitorInfo(w.hwnd)
+	if r == mi.Monitor {
+		w.config.Mode = Fullscreen
+	} else {
+		w.config.Mode = Windowed
+	}
+}
+
 func (w *window) Configure(options []Option) {
 	dpi := windows.GetSystemDPI()
 	cfg := configForDPI(dpi)
 	prev := w.config
+	w.updateWindowMode()
 	cnf := w.config
 	cnf.apply(cfg, options)