diff --git a/src/hb-ot-cmap-table.hh b/src/hb-ot-cmap-table.hh
index 3c6c87f..9f8818e 100644
--- a/src/hb-ot-cmap-table.hh
+++ b/src/hb-ot-cmap-table.hh
@@ -1898,6 +1898,8 @@
     bool get_nominal_glyph (hb_codepoint_t  unicode,
                             hb_codepoint_t *glyph) const
     {
+      if (unlikely (!this->get_glyph_funcZ)) return false;
+
       return this->get_glyph_funcZ (this->get_glyph_data, unicode, glyph);
     }