diff --git a/examples/windowsize/main.go b/examples/windowsize/main.go
index 3288c7440..addf12e72 100644
--- a/examples/windowsize/main.go
+++ b/examples/windowsize/main.go
@@ -231,7 +231,10 @@ func (g *game) Update(screen *ebiten.Image) error {
 	}
 	maximize := inpututil.IsKeyJustPressed(ebiten.KeyM)
 	minimize := inpututil.IsKeyJustPressed(ebiten.KeyN)
-	restore := inpututil.IsKeyJustPressed(ebiten.KeyE)
+	restore := false
+	if ebiten.IsWindowMaximized() || ebiten.IsWindowMinimized() {
+		restore = inpututil.IsKeyJustPressed(ebiten.KeyE)
+	}
 
 	if toUpdateWindowSize {
 		if *flagLegacy {
diff --git a/window.go b/window.go
index e00c5cd60..cdf119143 100644
--- a/window.go
+++ b/window.go
@@ -278,10 +278,15 @@ func MaximizeWindow() {
 
 // IsWindowMaximized reports whether the window is maximized or not.
 //
+// IsWindowMaximized returns false when the window is not resizable.
+//
 // IsWindowMaximized always returns false on browsers and mobiles.
 //
 // IsWindowMaximized is concurrent-safe.
 func IsWindowMaximized() bool {
+	if !IsWindowResizable() {
+		return false
+	}
 	if w := uiDriver().Window(); w != nil {
 		return w.IsMaximized()
 	}
@@ -315,8 +320,13 @@ func IsWindowMinimized() bool {
 
 // RestoreWindow restores the window from its maximized or minimized state.
 //
+// RestoreWindow panics when the window is not maximized nor minimized.
+//
 // RestoreWindow is concurrent-safe.
 func RestoreWindow() {
+	if !IsWindowMaximized() && !IsWindowMinimized() {
+		panic("ebiten: RestoreWindow must be called on a maximized or a minimized window")
+	}
 	if w := uiDriver().Window(); w != nil {
 		w.Restore()
 	}