diff --git a/src/backend/statistics/mvdistinct.c b/src/backend/statistics/mvdistinct.c
index 5df4e29..acc2d7e 100644
--- a/src/backend/statistics/mvdistinct.c
+++ b/src/backend/statistics/mvdistinct.c
@@ -161,10 +161,10 @@ statext_ndistinct_serialize(MVNDistinct *ndistinct)
 	Assert(ndistinct->type == STATS_NDISTINCT_TYPE_BASIC);
 
 	/*
-	 * Base size is base struct size, plus one base struct for each items,
-	 * including number of items for each.
+	 * Base size is size of scalar fields in the struct, plus one base struct
+	 * for each item, including number of items for each.
 	 */
-	len = VARHDRSZ + offsetof(MVNDistinct, items) +
+	len = VARHDRSZ + (3 * sizeof(uint32)) +
 		ndistinct->nitems * (offsetof(MVNDistinctItem, attrs) + sizeof(int));
 
 	/* and also include space for the actual attribute numbers */
@@ -182,9 +182,15 @@ statext_ndistinct_serialize(MVNDistinct *ndistinct)
 
 	tmp = VARDATA(output);
 
-	/* Store the base struct values */
-	memcpy(tmp, ndistinct, offsetof(MVNDistinct, items));
-	tmp += offsetof(MVNDistinct, items);
+	/* Store the base struct values (magic, type, nitems) */
+	memcpy(tmp, &ndistinct->magic, sizeof(uint32));
+	tmp += sizeof(uint32);
+
+	memcpy(tmp, &ndistinct->type, sizeof(uint32));
+	tmp += sizeof(uint32);
+
+	memcpy(tmp, &ndistinct->nitems, sizeof(uint32));
+	tmp += sizeof(uint32);
 
 	/*
 	 * store number of attributes and attribute numbers for each ndistinct
@@ -231,9 +237,10 @@ statext_ndistinct_deserialize(bytea *data)
 	if (data == NULL)
 		return NULL;
 
-	if (VARSIZE_ANY_EXHDR(data) < offsetof(MVNDistinct, items))
+	/* we expect at least the basic fields of MVNDistinct struct */
+	if (VARSIZE_ANY_EXHDR(data) < (3 * sizeof(uint32)))
 		elog(ERROR, "invalid MVNDistinct size %ld (expected at least %ld)",
-			 VARSIZE_ANY_EXHDR(data), offsetof(MVNDistinct, items));
+			 VARSIZE_ANY_EXHDR(data), 3 * sizeof(uint32));
 
 	/* read the MVNDistinct header */
 	ndistinct = (MVNDistinct *) palloc(sizeof(MVNDistinct));
@@ -241,18 +248,24 @@ statext_ndistinct_deserialize(bytea *data)
 	/* initialize pointer to the data part (skip the varlena header) */
 	tmp = VARDATA_ANY(data);
 
-	/* get the header and perform basic sanity checks */
-	memcpy(ndistinct, tmp, offsetof(MVNDistinct, items));
-	tmp += offsetof(MVNDistinct, items);
+	/* get the header fields and perform basic sanity checks */
+	memcpy(&ndistinct->magic, tmp, sizeof(uint32));
+	tmp += sizeof(uint32);
 
 	if (ndistinct->magic != STATS_NDISTINCT_MAGIC)
 		elog(ERROR, "invalid ndistinct magic %d (expected %d)",
 			 ndistinct->magic, STATS_NDISTINCT_MAGIC);
 
+	memcpy(&ndistinct->type, tmp, sizeof(uint32));
+	tmp += sizeof(uint32);
+
 	if (ndistinct->type != STATS_NDISTINCT_TYPE_BASIC)
 		elog(ERROR, "invalid ndistinct type %d (expected %d)",
 			 ndistinct->type, STATS_NDISTINCT_TYPE_BASIC);
 
+	memcpy(&ndistinct->nitems, tmp, sizeof(uint32));
+	tmp += sizeof(uint32);
+
 	Assert(ndistinct->nitems > 0);
 
 	/* what minimum bytea size do we expect for those parameters */