diff --git a/internal/glance/theme.go b/internal/glance/theme.go
index a3e26d4..07f3921 100644
--- a/internal/glance/theme.go
+++ b/internal/glance/theme.go
@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"html/template"
 	"net/http"
+	"time"
 )
 
 var (
@@ -29,6 +30,7 @@ func (a *application) handleThemeChangeRequest(w http.ResponseWriter, r *http.Re
 		Value:    themeKey,
 		Path:     a.Config.Server.BaseURL + "/",
 		SameSite: http.SameSiteLaxMode,
+		Expires:  time.Now().Add(2 * 365 * 24 * time.Hour),
 	})
 
 	w.Header().Set("Content-Type", "text/css")