diff --git a/gio/gseekable.c b/gio/gseekable.c
index 5b4460210..5237e7f2f 100644
--- a/gio/gseekable.c
+++ b/gio/gseekable.c
@@ -159,7 +159,7 @@ g_seekable_can_truncate (GSeekable *seekable)
 }
 
 /**
- * g_seekable_truncate:
+ * g_seekable_truncate: (virtual truncate_fn)
  * @seekable: a #GSeekable.
  * @offset: new length for @seekable, in bytes.
  * @cancellable: (nullable): optional #GCancellable object, %NULL to ignore.