diff --git a/src/backend/access/transam/subtrans.c b/src/backend/access/transam/subtrans.c
index 6a8e521f894..ce7c90aa38f 100644
--- a/src/backend/access/transam/subtrans.c
+++ b/src/backend/access/transam/subtrans.c
@@ -29,6 +29,7 @@
 #include "postgres.h"
 
 #include "access/slru.h"
+#include "access/parallel.h"
 #include "access/subtrans.h"
 #include "access/transam.h"
 #include "pg_trace.h"
@@ -152,6 +153,21 @@ SubTransGetTopmostTransaction(TransactionId xid)
 	TransactionId parentXid = xid,
 				previousXid = xid;
 
+	/*
+	 * We may have different xmins in active and transaction snapshots in
+	 * parallel workers. And TransactionXmin can be promoted to the max of them.
+	 * So, we do this to avoid assert below when restore active snapshot with
+	 * less xmin value.
+	 *
+	 * XXX: the same may be fixed by prohibiting read-only transactions (like
+	 * parallel scans) to increment TransactionXmin.
+	 */
+	if (IsParallelWorker())
+	{
+		xid = xid > TransactionXmin ? xid : TransactionXmin;
+		parentXid = xid;
+		previousXid = xid;
+	}
 	/* Can't ask about stuff that might not be around anymore */
 	Assert(TransactionIdFollowsOrEquals(xid, TransactionXmin));