diff --git a/doc/fixes37.0 b/doc/fixes37.0
index c0271d18b..1dfbf18c2 100644
--- a/doc/fixes37.0
+++ b/doc/fixes37.0
@@ -547,6 +547,8 @@ engraving with non-blade dulled the weapon anyway (pr #464)
 'sortdiscoveries:s' had a spurious generic header shown at the start of the
 	last class if there were any artifacts or unique items discovered
 loss of saddle by opening magic left hero mounted on unsaddled steed
+avoid segfault during error reporting for bad 'O' value(s) after theme rooms
+	have been initialized, leaving iflags.in_lua set
 
 curses: 'msg_window' option wasn't functional for curses unless the binary
 	also included tty support
diff --git a/src/files.c b/src/files.c
index c488ae93c..58ede76f8 100644
--- a/src/files.c
+++ b/src/files.c
@@ -2899,7 +2899,8 @@ config_erradd(const char *buf)
         buf = "Unknown error";
 
     if (iflags.in_lua) {
-        struct _config_error_errmsg *dat = (struct _config_error_errmsg *) alloc(sizeof (struct _config_error_errmsg));
+        struct _config_error_errmsg *dat
+                         = (struct _config_error_errmsg *) alloc(sizeof *dat);
 
         dat->next = config_error_msg;
         dat->line_num = config_error_data->line_num;
diff --git a/src/mklev.c b/src/mklev.c
index dde1b8165..dc606f7ad 100644
--- a/src/mklev.c
+++ b/src/mklev.c
@@ -277,6 +277,8 @@ makerooms(void)
             } else {
                 /* success; save state for this dungeon branch */
                 g.luathemes[u.uz.dnum] = (genericptr_t) themes;
+                /* keep themes context, so not 'nhl_done(themes);' */
+                iflags.in_lua = FALSE; /* can affect error messages */
             }
         }
         if (!themes) /* don't try again when making next level */
@@ -299,11 +301,11 @@ makerooms(void)
             }
         } else {
             if (themes) {
-                g.in_mk_themerooms = TRUE;
+                iflags.in_lua = g.in_mk_themerooms = TRUE;
                 g.themeroom_failed = FALSE;
                 lua_getglobal(themes, "themerooms_generate");
                 lua_call(themes, 0, 0);
-                g.in_mk_themerooms = FALSE;
+                iflags.in_lua = g.in_mk_themerooms = FALSE;
                 if (g.themeroom_failed
                     && ((themeroom_tries++ > 10)
                         || (g.nroom >= (MAXNROFROOMS / 6))))