diff --git a/libraries/AP_Filesystem/AP_Filesystem_config.h b/libraries/AP_Filesystem/AP_Filesystem_config.h
index 93e307ed7e269..beec2c506aadd 100644
--- a/libraries/AP_Filesystem/AP_Filesystem_config.h
+++ b/libraries/AP_Filesystem/AP_Filesystem_config.h
@@ -55,6 +55,13 @@
 #define AP_FILESYSTEM_FILE_READING_ENABLED (AP_FILESYSTEM_FILE_WRITING_ENABLED || AP_FILESYSTEM_ROMFS_ENABLED || AP_FILESYSTEM_SYS_ENABLED || AP_FILESYSTEM_PARAM_ENABLED)
 #endif
 
+// AP_FILESYSTEM_FILE_OPENDIR_ENABLED is true if you could expect to
+// be able to open and read a non-virtual directory.  Notably this excludes
+// virtual files like SYSFS, and the magic param/mission upload targets.
+#ifndef AP_FILESYSTEM_FILE_OPENDIR_ENABLED
+#define AP_FILESYSTEM_FILE_OPENDIR_ENABLED (AP_FILESYSTEM_FILE_WRITING_ENABLED || AP_FILESYSTEM_ROMFS_ENABLED)
+#endif
+
 #ifndef AP_FILESYSTEM_SYS_FLASH_ENABLED
 #define AP_FILESYSTEM_SYS_FLASH_ENABLED CONFIG_HAL_BOARD == HAL_BOARD_CHIBIOS
 #endif