diff --git a/doc/fixes3-7-0.txt b/doc/fixes3-7-0.txt
index 7fba2fda7..83fc4c1da 100644
--- a/doc/fixes3-7-0.txt
+++ b/doc/fixes3-7-0.txt
@@ -2619,6 +2619,8 @@ fix msg_window:combination and TTY getlin() ^P (pr #1155 by entrez)
 remove a null sobj check from gold_detect that was situated after
 	dereferences had already been done (pr #1173 by argrath) and
 	adjust prototype in extern.h
+check for valid indexes of def_monsyms[] and def_oc_syms[] in
+	choose_classes_menu() (pr #1179 by argrath)
 
 
 Code Cleanup and Reorganization
diff --git a/src/windows.c b/src/windows.c
index e67cca41d..b3ddc3dfa 100644
--- a/src/windows.c
+++ b/src/windows.c
@@ -1665,10 +1665,12 @@ choose_classes_menu(const char *prompt,
     start_menu(win, MENU_BEHAVE_STANDARD);
     while (*class_list) {
         int idx;
+
         selected = FALSE;
         switch (category) {
         case 0:
-            if ((idx = def_char_to_monclass(*class_list)) == MAXMCLASSES) {
+            idx = def_char_to_monclass(*class_list);
+            if (!IndexOk(idx, def_monsyms)) {
                 panic("choose_classes_menu: invalid monclass '%c'", *class_list);
                 /*NOTREACHED*/
             }
@@ -1677,7 +1679,8 @@ choose_classes_menu(const char *prompt,
             Sprintf(buf, "%s", text);
             break;
         case 1:
-            if ((idx = def_char_to_objclass(*class_list)) == MAXOCLASSES) {
+            idx = def_char_to_objclass(*class_list);
+            if (!IndexOk(idx, def_oc_syms)) {
                 panic("choose_classes_menu: invalid objclass '%c'", *class_list);
                 /*NOTREACHED*/
             }