diff --git a/demux/demux_mkv_timeline.c b/demux/demux_mkv_timeline.c
index 2a02a35dc5..32eab2ca8f 100644
--- a/demux/demux_mkv_timeline.c
+++ b/demux/demux_mkv_timeline.c
@@ -517,7 +517,7 @@ void build_ordered_chapter_timeline(struct timeline *tl)
         .global = tl->global,
         .tl = tl,
         .demuxer = demuxer,
-        .opts = mp_get_config_group(ctx, tl->global, NULL),
+        .opts = mp_get_config_group(ctx, tl->global, GLOBAL_CONFIG),
     };
 
     if (!ctx->opts->ordered_chapters || !demuxer->access_references) {
diff --git a/options/m_config.h b/options/m_config.h
index 19da75e83c..40cd367613 100644
--- a/options/m_config.h
+++ b/options/m_config.h
@@ -278,15 +278,17 @@ struct m_config_cache {
     void *wakeup_cb_ctx;
 };
 
+#define GLOBAL_CONFIG NULL
+
 // Create a mirror copy from the global options.
 // Keep in mind that a m_config_cache object is not thread-safe; it merely
 // provides thread-safe access to the global options. All API functions for
 // the same m_config_cache object must synchronized, unless otherwise noted.
 //  ta_parent: parent for the returned allocation
 //  global: option data source
-//  group: the option group to return. This can be NULL for the global option
-//         struct (MPOpts), or m_sub_options used in a certain OPT_SUBSTRUCT()
-//         item.
+//  group: the option group to return. This can be GLOBAL_CONFIG for the global
+//         option struct (MPOpts), or m_sub_options used in a certain
+//         OPT_SUBSTRUCT() item.
 struct m_config_cache *m_config_cache_alloc(void *ta_parent,
                                             struct mpv_global *global,
                                             const struct m_sub_options *group);
@@ -317,7 +319,7 @@ bool m_config_cache_update(struct m_config_cache *cache);
 // Like m_config_cache_alloc(), but return the struct (m_config_cache->opts)
 // directly, with no way to update the config. Basically this returns a copy
 // with a snapshot of the current option values.
-// group==NULL is a special case, and always returns the root group.
+// group==GLOBAL_CONFIG is a special case, and always returns the root group.
 void *mp_get_config_group(void *ta_parent, struct mpv_global *global,
                           const struct m_sub_options *group);