diff --git a/lib/config.cc b/lib/config.cc
index d14f5422..fe67ef41 100644
--- a/lib/config.cc
+++ b/lib/config.cc
@@ -464,3 +464,8 @@ notmuch_config_set (notmuch_database_t *notmuch, notmuch_config_key_t key, const
 
     return notmuch_database_set_config (notmuch, _notmuch_config_key_to_string (key), val);
 }
+
+void
+_notmuch_config_cache (notmuch_database_t *notmuch, notmuch_config_key_t key, const char *val) {
+    _notmuch_string_map_set (notmuch->config, _notmuch_config_key_to_string (key), val);
+}
diff --git a/lib/notmuch-private.h b/lib/notmuch-private.h
index 961d50cf..5e0b42e3 100644
--- a/lib/notmuch-private.h
+++ b/lib/notmuch-private.h
@@ -713,6 +713,10 @@ _notmuch_config_load_from_file (notmuch_database_t * db, GKeyFile *file);
 
 notmuch_status_t
 _notmuch_config_load_defaults (notmuch_database_t * db);
+
+void
+_notmuch_config_cache (notmuch_database_t *db, notmuch_config_key_t key, const char* val);
+
 NOTMUCH_END_DECLS
 
 #ifdef __cplusplus