diff --git a/src/hb-ot-cff1-table.hh b/src/hb-ot-cff1-table.hh
index ce97182e1..4aa337f78 100644
--- a/src/hb-ot-cff1-table.hh
+++ b/src/hb-ot-cff1-table.hh
@@ -406,6 +406,8 @@ struct Charset1_2 {
   void collect_glyph_to_sid_map (hb_map_t *mapping, unsigned int num_glyphs) const
   {
     hb_codepoint_t gid = 1;
+    if (gid >= num_glyphs)
+      return;
     for (unsigned i = 0;; i++)
     {
       hb_codepoint_t sid = ranges[i].first;