diff --git a/src/backend/utils/adt/tsvector.c b/src/backend/utils/adt/tsvector.c
index b02fecc081..62f0926d86 100644
--- a/src/backend/utils/adt/tsvector.c
+++ b/src/backend/utils/adt/tsvector.c
@@ -491,7 +491,7 @@ tsvectorrecv(PG_FUNCTION_ARGS)
 		 * But make sure the buffer is large enough first.
 		 */
 		while (hdrlen + SHORTALIGN(datalen + lex_len) +
-			   (npos + 1) * sizeof(WordEntryPos) >= len)
+			   sizeof(uint16) + npos * sizeof(WordEntryPos) >= len)
 		{
 			len *= 2;
 			vec = (TSVector) repalloc(vec, len);
@@ -537,7 +537,7 @@ tsvectorrecv(PG_FUNCTION_ARGS)
 					elog(ERROR, "position information is misordered");
 			}
 
-			datalen += (npos + 1) * sizeof(WordEntry);
+			datalen += sizeof(uint16) + npos * sizeof(WordEntryPos);
 		}
 	}