diff --git a/src/disptab.h b/src/disptab.h
index 3458105b9a7..6ee008453df 100644
--- a/src/disptab.h
+++ b/src/disptab.h
@@ -33,7 +33,8 @@ Boston, MA 02111-1307, USA.  */
 #define DISP_INVIS_VECTOR(dp) ((dp)->extras[4])
 #define DISP_BORDER_GLYPH(dp) ((dp)->extras[5])
 
-#define DISP_CHAR_VECTOR(dp, c) ((c) < 0x80 ? (dp)->contents[c] : Qnil)
+#define DISP_CHAR_VECTOR(dp, c) \
+  (SINGLE_BYTE_CHAR_P(c) ? (dp)->contents[c] : Qnil)
 
 /* Defined in window.c.  */
 extern struct Lisp_Char_Table *window_display_table ();