diff --git a/src/backend/utils/adt/txid.c b/src/backend/utils/adt/txid.c
index a005e67..44f7880 100644
*** a/src/backend/utils/adt/txid.c
--- b/src/backend/utils/adt/txid.c
*************** cmp_txid(const void *aa, const void *bb)
*** 131,146 ****
  }
  
  /*
!  * sort a snapshot's txids, so we can use bsearch() later.
   *
   * For consistency of on-disk representation, we always sort even if bsearch
!  * will not be used.
   */
  static void
  sort_snapshot(TxidSnapshot *snap)
  {
  	if (snap->nxip > 1)
  		qsort(snap->xip, snap->nxip, sizeof(txid), cmp_txid);
  }
  
  /*
--- 131,161 ----
  }
  
  /*
!  * unique sort a snapshot's txids, so we can use bsearch() later.
   *
   * For consistency of on-disk representation, we always sort even if bsearch
!  * will not be used. 
   */
  static void
  sort_snapshot(TxidSnapshot *snap)
  {
+ 	txid	last = 0;
+ 	int		nxip, idx1, idx2;
+ 
  	if (snap->nxip > 1)
+ 	{
  		qsort(snap->xip, snap->nxip, sizeof(txid), cmp_txid);
+ 		nxip = snap->nxip;
+ 		idx1 = idx2 = 0;
+ 		while (idx1 < nxip)
+ 		{
+ 			if (snap->xip[idx1] != last)
+ 				last = snap->xip[idx2++] = snap->xip[idx1];
+ 			else
+ 				snap->nxip--;
+ 			idx1++;
+ 		}
+ 	}
  }
  
  /*
*************** parse_snapshot(const char *str)
*** 294,304 ****
  		val = str2txid(str, &endp);
  		str = endp;
  
! 		/* require the input to be in order */
! 		if (val < xmin || val >= xmax || val <= last_val)
  			goto bad_format;
  
! 		buf_add_txid(buf, val);
  		last_val = val;
  
  		if (*str == ',')
--- 309,320 ----
  		val = str2txid(str, &endp);
  		str = endp;
  
! 		/* require the input to be in order and skip duplicates */
! 		if (val < xmin || val >= xmax || val < last_val)
  			goto bad_format;
  
! 		if (val != last_val)
! 			buf_add_txid(buf, val);
  		last_val = val;
  
  		if (*str == ',')
diff --git a/src/test/regress/expected/txid.out b/src/test/regress/expected/txid.out
index 930b86a..7750b7b 100644
*** a/src/test/regress/expected/txid.out
--- b/src/test/regress/expected/txid.out
*************** select '12:18:14,16'::txid_snapshot;
*** 12,17 ****
--- 12,23 ----
   12:18:14,16
  (1 row)
  
+ select '12:16:14,14'::txid_snapshot;
+  txid_snapshot 
+ ---------------
+  12:16:14
+ (1 row)
+ 
  -- errors
  select '31:12:'::txid_snapshot;
  ERROR:  invalid input for txid_snapshot: "31:12:"
*************** select '12:16:14,13'::txid_snapshot;
*** 29,38 ****
  ERROR:  invalid input for txid_snapshot: "12:16:14,13"
  LINE 1: select '12:16:14,13'::txid_snapshot;
                 ^
- select '12:16:14,14'::txid_snapshot;
- ERROR:  invalid input for txid_snapshot: "12:16:14,14"
- LINE 1: select '12:16:14,14'::txid_snapshot;
-                ^
  create temp table snapshot_test (
  	nr	integer,
  	snap	txid_snapshot
--- 35,40 ----
diff --git a/src/test/regress/sql/txid.sql b/src/test/regress/sql/txid.sql
index ecae10e..b6650b9 100644
*** a/src/test/regress/sql/txid.sql
--- b/src/test/regress/sql/txid.sql
***************
*** 3,15 ****
  -- i/o
  select '12:13:'::txid_snapshot;
  select '12:18:14,16'::txid_snapshot;
  
  -- errors
  select '31:12:'::txid_snapshot;
  select '0:1:'::txid_snapshot;
  select '12:13:0'::txid_snapshot;
  select '12:16:14,13'::txid_snapshot;
- select '12:16:14,14'::txid_snapshot;
  
  create temp table snapshot_test (
  	nr	integer,
--- 3,15 ----
  -- i/o
  select '12:13:'::txid_snapshot;
  select '12:18:14,16'::txid_snapshot;
+ select '12:16:14,14'::txid_snapshot;
  
  -- errors
  select '31:12:'::txid_snapshot;
  select '0:1:'::txid_snapshot;
  select '12:13:0'::txid_snapshot;
  select '12:16:14,13'::txid_snapshot;
  
  create temp table snapshot_test (
  	nr	integer,