diff --git a/src/hb-buffer.hh b/src/hb-buffer.hh
index b5596d945..6c771774a 100644
--- a/src/hb-buffer.hh
+++ b/src/hb-buffer.hh
@@ -386,7 +386,7 @@ struct hb_buffer_t
     inf.cluster = cluster;
   }
 
-  int
+  unsigned int
   _unsafe_to_break_find_min_cluster (const hb_glyph_info_t *infos,
 				     unsigned int start, unsigned int end,
 				     unsigned int cluster) const