diff --git a/src/backend/access/heap/vacuumlazy.c b/src/backend/access/heap/vacuumlazy.c
index fe2a6062b9c..e1bb97951b0 100644
--- a/src/backend/access/heap/vacuumlazy.c
+++ b/src/backend/access/heap/vacuumlazy.c
@@ -3482,6 +3482,12 @@ parallel_vacuum_main(dsm_segment *seg, shm_toc *toc)
 	LVRelStats	vacrelstats;
 	ErrorContextCallback errcallback;
 
+	/*
+	 * A parallel vacuum worker must have only PROC_IN_VACUUM flag since we
+	 * don't support parallel vacuum for autovacuum as of now.
+	 */
+	Assert(MyPgXact->vacuumFlags == PROC_IN_VACUUM);
+
 	lvshared = (LVShared *) shm_toc_lookup(toc, PARALLEL_VACUUM_KEY_SHARED,
 										   false);
 	elevel = lvshared->elevel;
diff --git a/src/backend/storage/ipc/procarray.c b/src/backend/storage/ipc/procarray.c
index 828ed2a38a1..2f1d4af17a5 100644
--- a/src/backend/storage/ipc/procarray.c
+++ b/src/backend/storage/ipc/procarray.c
@@ -1864,6 +1864,10 @@ ProcArrayInstallImportedXmin(TransactionId xmin,
  * PGPROC of the transaction from which we imported the snapshot, rather than
  * an XID.
  *
+ * Note that this function also copies vacuumFlags from the source `proc` in
+ * order to avoid the case where MyPgXact's xmin needs to be skipped for
+ * computing xid horizon.
+ *
  * Returns true if successful, false if source xact is no longer running.
  */
 bool
@@ -1876,8 +1880,10 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
 	Assert(TransactionIdIsNormal(xmin));
 	Assert(proc != NULL);
 
-	/* Get lock so source xact can't end while we're doing this */
-	LWLockAcquire(ProcArrayLock, LW_SHARED);
+	/*
+	 * Get an exclusive lock so that we can copy vacuumFlags from source proc.
+	 */
+	LWLockAcquire(ProcArrayLock, LW_EXCLUSIVE);
 
 	pgxact = &allPgXact[proc->pgprocno];
 
@@ -1892,7 +1898,13 @@ ProcArrayInstallRestoredXmin(TransactionId xmin, PGPROC *proc)
 		TransactionIdIsNormal(xid) &&
 		TransactionIdPrecedesOrEquals(xid, xmin))
 	{
+		/* Install xmin */
 		MyPgXact->xmin = TransactionXmin = xmin;
+
+		/* Flags being copied must be valid copy-able flags. */
+		Assert((pgxact->vacuumFlags & (~PROC_COPYABLE_FLAGS)) == 0);
+		MyPgXact->vacuumFlags = pgxact->vacuumFlags;
+
 		result = true;
 	}
 
diff --git a/src/include/storage/proc.h b/src/include/storage/proc.h
index 1ee9000b2b9..b3ea1a25860 100644
--- a/src/include/storage/proc.h
+++ b/src/include/storage/proc.h
@@ -62,6 +62,13 @@ struct XidCache
 #define		PROC_VACUUM_STATE_MASK \
 	(PROC_IN_VACUUM | PROC_IN_ANALYZE | PROC_VACUUM_FOR_WRAPAROUND)
 
+/*
+ * Flags that are valid to copy from another proc, the parallel leader
+ * process in practice.  Currently, a flag that is set during parallel
+ * vacuum is allowed.
+ */
+#define		PROC_COPYABLE_FLAGS (PROC_IN_VACUUM)
+
 /*
  * We allow a small number of "weak" relation locks (AccessShareLock,
  * RowShareLock, RowExclusiveLock) to be recorded in the PGPROC structure