diff --git a/include/extern.h b/include/extern.h
index 9977353a8..ee6862776 100644
--- a/include/extern.h
+++ b/include/extern.h
@@ -1005,7 +1005,9 @@ extern boolean can_read_file(const char *) NONNULLARG1;
 extern void config_error_init(boolean, const char *, boolean);
 extern void config_erradd(const char *);
 extern int config_error_done(void);
-extern boolean read_config_file(const char *, int) NONNULLARG1;
+/* arg1 of read_config_file can be NULL to pass through
+ * to fopen_config_file() to mean 'use the default config file name' */
+extern boolean read_config_file(const char *, int);
 extern void check_recordfile(const char *);
 extern void read_wizkit(void);
 extern boolean parse_conf_str(const char *str, boolean (*proc)(char *));