--- src/hb-ot-hmtx-table.hh
+++ src/hb-ot-hmtx-table.hh
@@ -143,7 +143,7 @@
 	  return default_advance;
       }
 
-      return table->longMetric[MIN (glyph, (uint32_t) num_advances - 1)].advance
+      return static_cast<OT::LongMetric const *>(table->longMetric)[MIN (glyph, (uint32_t) num_advances - 1)].advance
 	   + var_table->get_advance_var (glyph, font->coords, font->num_coords); // TODO Optimize?!
     }