diff --git a/src/hb-ot-cff1-table.hh b/src/hb-ot-cff1-table.hh
index c68763fe4..8717b4a5a 100644
--- a/src/hb-ot-cff1-table.hh
+++ b/src/hb-ot-cff1-table.hh
@@ -1344,6 +1344,7 @@ struct cff1
     bool get_glyph_name (hb_codepoint_t glyph,
 			 char *buf, unsigned int buf_len) const
     {
+      if (unlikely (glyph >= num_glyphs)) return false;
       if (unlikely (!is_valid ())) return false;
       if (is_CID()) return false;
       if (unlikely (!buf_len)) return true;