diff --git a/src/buffer.cc b/src/buffer.cc
index 93808fd6..c0167193 100644
--- a/src/buffer.cc
+++ b/src/buffer.cc
@@ -514,7 +514,7 @@ void Buffer::set_fs_timestamp(time_t ts)
 void Buffer::on_option_changed(const Option& option)
 {
     run_hook_in_own_context("BufSetOption",
-                            option.name() + "=" + option.get_as_string());
+                            format("{}={}", option.name(), option.get_as_string()));
 }
 
 void Buffer::run_hook_in_own_context(StringView hook_name, StringView param)
diff --git a/src/window.cc b/src/window.cc
index b23fcdd8..1c205d8d 100644
--- a/src/window.cc
+++ b/src/window.cc
@@ -285,8 +285,8 @@ ByteCoordAndTarget Window::offset_coord(ByteCoordAndTarget coord, LineCount offs
 
 void Window::on_option_changed(const Option& option)
 {
-    String desc = option.name() + "=" + option.get_as_string();
-    run_hook_in_own_context("WinSetOption", desc);
+    run_hook_in_own_context("WinSetOption",
+                            format("{}={}", option.name(), option.get_as_string()));
 
     // an highlighter might depend on the option, so we need to redraw
     forget_timestamp();