diff --git a/theme.go b/theme.go
index b5e42a3..a7f15fa 100644
--- a/theme.go
+++ b/theme.go
@@ -2,6 +2,7 @@
 package mujica
 
 import (
+	"fmt"
 	"time"
 
 	"github.com/egoist/mygo/ui"
@@ -51,6 +52,15 @@ type themeKey struct{}
 
 // Use applies s to the window. Call it first in every frame of the view.
 func Use(c *ui.Context, s Settings) {
+	if s.Mode < System || s.Mode > Dark {
+		panic(fmt.Sprintf("mujica: invalid Mode %d", s.Mode))
+	}
+	if s.Density < theme.Default || s.Density > theme.Comfortable {
+		panic(fmt.Sprintf("mujica: invalid Density %d", s.Density))
+	}
+	if s.Locale != "" && s.Locale != EnUS && s.Locale != ZhCN {
+		panic("mujica: unsupported Locale " + string(s.Locale))
+	}
 	dark := c.Theme().Dark
 	switch s.Mode {
 	case Light:
@@ -99,6 +109,7 @@ func Use(c *ui.Context, s Settings) {
 		Spacing:        s.Density.Unit(),
 		FontSize:       size,
 	})
+	c.Root().LineHeight(theme.LineHeight)
 	*ui.Local(c.Root(), themeKey{}, func() windowTheme { return windowTheme{} }) = windowTheme{k, s.Density, s.Locale, s.Messages, true}
 }
 
diff --git a/theme_test.go b/theme_test.go
new file mode 100644
index 0000000..59c0bb0
--- /dev/null
+++ b/theme_test.go
@@ -0,0 +1,43 @@
+package mujica
+
+import (
+	"testing"
+
+	"github.com/egoist/mygo/ui"
+
+	"mujicaui/theme"
+)
+
+func TestUseLineHeight(t *testing.T) {
+	var h float32
+	tt := ui.NewTester(func(c *ui.Context) {
+		Use(c, Settings{})
+		h = ui.Text(c, "one\ntwo").Bounds().H
+	}, 300, 200)
+	tt.Frame()
+	if want := 2 * theme.BodySize * theme.LineHeight; h < want-0.5 || h > want+0.5 {
+		t.Fatalf("two lines are %v DIPs, want %v", h, want)
+	}
+}
+
+func TestUseRejectsInvalidSettings(t *testing.T) {
+	for _, s := range []Settings{{Mode: 9}, {Density: 9}, {Locale: "fr-FR"}} {
+		func() {
+			defer func() {
+				if recover() == nil {
+					t.Errorf("%+v accepted", s)
+				}
+			}()
+			ui.NewTester(func(c *ui.Context) { Use(c, s) }, 100, 100)
+		}()
+	}
+}
+
+func TestTokensWithoutUsePanics(t *testing.T) {
+	defer func() {
+		if recover() == nil {
+			t.Fatal("Tokens before Use did not panic")
+		}
+	}()
+	ui.NewTester(func(c *ui.Context) { Tokens(c) }, 100, 100)
+}