diff --git a/contrib/ltree/crc32.c b/contrib/ltree/crc32.c
index d21bed31fdd..1269e707ee5 100644
--- a/contrib/ltree/crc32.c
+++ b/contrib/ltree/crc32.c
@@ -32,13 +32,14 @@ ltree_crc32_sz(const char *buf, int size)
 	INIT_TRADITIONAL_CRC32(crc);
 	while (size > 0)
 	{
-		char		foldstr[UNICODE_CASEMAP_BUFSZ];
+		/* max space required to map single codepoint, including NUL */
+		char		foldstr[UNICODE_CASEMAP_BUFSZ + 1];
 		int			srclen = pg_mblen_range(p, end);
 		size_t		foldlen;
 
 		/* fold one codepoint at a time */
-		foldlen = pg_strfold(foldstr, UNICODE_CASEMAP_BUFSZ, p, srclen,
-							 locale);
+		foldlen = pg_strfold(foldstr, sizeof(foldstr), p, srclen, locale);
+		Assert(foldlen < sizeof(foldstr));
 
 		COMP_TRADITIONAL_CRC32(crc, foldstr, foldlen);