diff --git a/include/display.h b/include/display.h
index ab69aaece..a427d1e1b 100644
--- a/include/display.h
+++ b/include/display.h
@@ -711,27 +711,29 @@ enum glyph_offsets {
      && (glyph) < (GLYPH_CMAP_C_OFF + ((S_goodpos - S_digbeam) + 1)))
 
 #define glyph_to_cmap(glyph) \
-    (((glyph) == GLYPH_CMAP_STONE_OFF)                                 \
-      ? S_stone                                                        \
-      : glyph_is_cmap_main(glyph)                                      \
-        ? (((glyph) - GLYPH_CMAP_MAIN_OFF) + S_vwall)                  \
-        : glyph_is_cmap_mines(glyph)                                   \
-          ? (((glyph) - GLYPH_CMAP_MINES_OFF) + S_vwall)               \
-          : glyph_is_cmap_gehennom(glyph)                              \
-            ? (((glyph) - GLYPH_CMAP_GEH_OFF) + S_vwall)               \
-            : glyph_is_cmap_knox(glyph)                                \
-              ? (((glyph) - GLYPH_CMAP_KNOX_OFF) + S_vwall)            \
-              : glyph_is_cmap_sokoban(glyph)                           \
-                ? (((glyph) - GLYPH_CMAP_SOKO_OFF) + S_vwall)          \
-                : glyph_is_cmap_a(glyph)                               \
-                  ? (((glyph) - GLYPH_CMAP_A_OFF) + S_ndoor)           \
-                  : glyph_is_cmap_altar(glyph)                         \
-                    ? (S_altar)                                        \
-                    : glyph_is_cmap_b(glyph)                           \
-                      ? (((glyph) - GLYPH_CMAP_B_OFF) + S_grave)       \
-                      : glyph_is_cmap_c(glyph)                         \
-                        ? (((glyph) - GLYPH_CMAP_C_OFF) + S_digbeam)   \
-                        : NO_GLYPH)
+    (((glyph) == GLYPH_CMAP_STONE_OFF)                                  \
+      ? S_stone                                                         \
+      : glyph_is_cmap_main(glyph)                                       \
+        ? (((glyph) - GLYPH_CMAP_MAIN_OFF) + S_vwall)                   \
+        : glyph_is_cmap_mines(glyph)                                    \
+          ? (((glyph) - GLYPH_CMAP_MINES_OFF) + S_vwall)                \
+          : glyph_is_cmap_gehennom(glyph)                               \
+            ? (((glyph) - GLYPH_CMAP_GEH_OFF) + S_vwall)                \
+            : glyph_is_cmap_knox(glyph)                                 \
+              ? (((glyph) - GLYPH_CMAP_KNOX_OFF) + S_vwall)             \
+              : glyph_is_cmap_sokoban(glyph)                            \
+                ? (((glyph) - GLYPH_CMAP_SOKO_OFF) + S_vwall)           \
+                : glyph_is_cmap_a(glyph)                                \
+                  ? (((glyph) - GLYPH_CMAP_A_OFF) + S_ndoor)            \
+                  : glyph_is_cmap_altar(glyph)                          \
+                    ? (S_altar)                                         \
+                    : glyph_is_cmap_b(glyph)                            \
+                      ? (((glyph) - GLYPH_CMAP_B_OFF) + S_grave)        \
+                      : glyph_is_cmap_c(glyph)                          \
+                        ? (((glyph) - GLYPH_CMAP_C_OFF) + S_digbeam)    \
+                        : glyph_is_cmap_zap(glyph)                      \
+                          ? ((((glyph) - GLYPH_ZAP_OFF) % 4) + S_vbeam) \
+                          : NO_GLYPH)
 
 #define glyph_to_swallow(glyph) \
     (glyph_is_swallow(glyph) ? (((glyph) - GLYPH_SWALLOW_OFF) & 0x7) : 0)
diff --git a/src/cmd.c b/src/cmd.c
index 3e875eef3..917bb3127 100644
--- a/src/cmd.c
+++ b/src/cmd.c
@@ -4026,6 +4026,13 @@ wiz_display_macros(void)
                         glyph, test);
                  putstr(win, 0, buf);
             }
+            if (glyph_is_cmap_zap(glyph)
+                && !(test >= S_vbeam && test <= S_rslant)) {
+                Sprintf(buf,
+                        "glyph_is_zap(glyph=%d) returned non-zap cmap %d",
+                        glyph, test);
+                 putstr(win, 0, buf);
+            }
             /* check against defsyms array subscripts */
             if (test < 0 || test >= SIZE(defsyms)) {
                 if (!trouble++)