diff --git a/src/default/spiffs_config.h b/src/default/spiffs_config.h
index 6b95a35..d675f2b 100644
--- a/src/default/spiffs_config.h
+++ b/src/default/spiffs_config.h
@@ -110,6 +110,13 @@
 // Maximum length of the metadata associated with an object.
 // Setting to non-zero value enables metadata-related API but also
 // changes the on-disk format, so the change is not backward-compatible.
+//
+// Do note: the meta length must never exceed
+// logical_page_size - (SPIFFS_OBJ_NAME_LEN + 64)
+//
+// This is derived from following:
+// logical_page_size - (SPIFFS_OBJ_NAME_LEN + sizeof(spiffs_page_header) +
+// spiffs_object_ix_header fields + at least some LUT entries)
 #ifndef SPIFFS_OBJ_META_LEN
 #define SPIFFS_OBJ_META_LEN             (0)
 #endif