diff --git a/include/clap/ext/draft/undo.h b/include/clap/ext/draft/undo.h
index 4c9ee28a..76070c38 100644
--- a/include/clap/ext/draft/undo.h
+++ b/include/clap/ext/draft/undo.h
@@ -51,16 +51,19 @@ extern "C" {
 /// capture a plugin state for the undo step.
 
 typedef struct clap_undo_delta_properties {
+   // If true, then the plugin will provide deltas in host->change_made().
    // If false, then all clap_undo_delta_properties's attributes become irrelevant.
-   // If set, then the plugin will provide deltas in host->change_made().
    bool has_delta;
 
-   // If set, then the delta will be reusable in the future as long as the plugin is
-   // compatible with the given format_version.
+   // If true, then the deltas can be stored on disk and re-used in the future as long as the plugin
+   // is compatible with the given format_version.
+   //
+   // If false, then format_version must be set to CLAP_INVALID_ID.
    bool are_deltas_persistent;
 
    // This represents the delta format version that the plugin is currently using.
-   uint32_t format_version;
+   // Use CLAP_INVALID_ID for invalid value.
+   clap_id format_version;
 } clap_undo_delta_properties_t;
 
 // Use CLAP_EXT_UNDO_DELTA.