diff --git a/handler.go b/handler.go
index 6c34f2f..0dd2dae 100644
--- a/handler.go
+++ b/handler.go
@@ -51,7 +51,7 @@ func New(packfile string) (*Handler, error) {
 	}
 
 	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Frame-Options
-	h.SetHeader("X-Frame-Options", "sameorigin")
+	h.SetHeader("X-Frame-Options", "SAMEORIGIN")
 
 	// https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/X-Content-Type-Options
 	h.SetHeader("X-Content-Type-Options", "nosniff")