diff --git a/src/include/postgres.h b/src/include/postgres.h
index f9c5527..5f8ada6 100644
--- a/src/include/postgres.h
+++ b/src/include/postgres.h
@@ -267,6 +267,7 @@ typedef struct
 	 (VARATT_IS_1B(PTR) ? VARSIZE_1B(PTR) : \
 	  VARSIZE_4B(PTR)))
 
+/* Size of a varlena data, excluding header */
 #define VARSIZE_ANY_EXHDR(PTR) \
 	(VARATT_IS_1B_E(PTR) ? VARSIZE_1B_E(PTR)-VARHDRSZ_EXTERNAL : \
 	 (VARATT_IS_1B(PTR) ? VARSIZE_1B(PTR)-VARHDRSZ_SHORT : \