diff --git a/src/backend/replication/logical/reorderbuffer.c b/src/backend/replication/logical/reorderbuffer.c
index 46e66608cf..4e452cce7c 100644
--- a/src/backend/replication/logical/reorderbuffer.c
+++ b/src/backend/replication/logical/reorderbuffer.c
@@ -3326,6 +3326,26 @@ ReorderBufferXidHasBaseSnapshot(ReorderBuffer *rb, TransactionId xid)
 }
 
 
+/*
+ * ReorderBufferXidIsKnownSubXact
+ *		Returns true if the xid is a known subtransaction.
+ */
+bool
+ReorderBufferXidIsKnownSubXact(ReorderBuffer *rb, TransactionId xid)
+{
+	ReorderBufferTXN *txn;
+
+	txn = ReorderBufferTXNByXid(rb, xid, false,
+								NULL, InvalidXLogRecPtr, false);
+
+	/* a known subtxn? */
+	if (txn && rbtxn_is_known_subxact(txn))
+		return true;
+
+	return false;
+}
+
+
 /*
  * ---------------------------------------
  * Disk serialization support
diff --git a/src/backend/replication/logical/snapbuild.c b/src/backend/replication/logical/snapbuild.c
index a5333349a8..12d283f4de 100644
--- a/src/backend/replication/logical/snapbuild.c
+++ b/src/backend/replication/logical/snapbuild.c
@@ -591,12 +591,18 @@ SnapBuildInitialSnapshot(SnapBuild *builder)
 
 		if (test == NULL)
 		{
-			if (newxcnt >= GetMaxSnapshotXidCount())
-				ereport(ERROR,
-						(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
-						 errmsg("initial slot snapshot too large")));
+			bool issubxact =
+				ReorderBufferXidIsKnownSubXact(builder->reorder, xid);
 
-			newxip[newxcnt++] = xid;
+			if (!issubxact)
+			{				
+				if (newxcnt >= GetMaxSnapshotXidCount())
+					ereport(ERROR,
+							(errcode(ERRCODE_T_R_SERIALIZATION_FAILURE),
+							 errmsg("initial slot snapshot too large")));
+				
+				newxip[newxcnt++] = xid;
+			}
 		}
 
 		TransactionIdAdvance(xid);
diff --git a/src/include/replication/reorderbuffer.h b/src/include/replication/reorderbuffer.h
index 5b40ff75f7..e5fa1051d7 100644
--- a/src/include/replication/reorderbuffer.h
+++ b/src/include/replication/reorderbuffer.h
@@ -669,6 +669,7 @@ void		ReorderBufferXidSetCatalogChanges(ReorderBuffer *, TransactionId xid, XLog
 bool		ReorderBufferXidHasCatalogChanges(ReorderBuffer *, TransactionId xid);
 bool		ReorderBufferXidHasBaseSnapshot(ReorderBuffer *, TransactionId xid);
 
+bool		ReorderBufferXidIsKnownSubXact(ReorderBuffer *rb, TransactionId xid);
 bool		ReorderBufferRememberPrepareInfo(ReorderBuffer *rb, TransactionId xid,
 											 XLogRecPtr prepare_lsn, XLogRecPtr end_lsn,
 											 TimestampTz prepare_time,