*** a/src/backend/access/nbtree/nbtree.c
--- b/src/backend/access/nbtree/nbtree.c
***************
*** 585,614 **** btrestrpos(PG_FUNCTION_ARGS)
  	if (so->markItemIndex >= 0)
  	{
  		/*
! 		 * The mark position is on the same page we are currently on. Just
  		 * restore the itemIndex.
  		 */
  		so->currPos.itemIndex = so->markItemIndex;
  	}
! 	else
  	{
  		/*
! 		 * The scan moved to a new page after the mark, and we are now
! 		 * restoring to the marked page.  We aren't holding any read locks,
! 		 * but if we're still holding the pin for the current position, we
! 		 * must drop it.
  		 *
! 		 * NB: This must deal with the possibility that so->markItemIndex < 0
! 		 * but so->currPos == so->markPos.  This would be an unusual case,
! 		 * where the scan moved to a new index page after the mark, restored,
! 		 * and later restored again without setting a new mark or moving off
! 		 * the page again.
  		 */
  		if (BTScanPosIsValid(so->currPos))
  		{
  			/* Before leaving current page, deal with any killed items */
! 			if (so->numKilled > 0 &&
! 				so->currPos.currPage != so->markPos.currPage)
  				_bt_killitems(scan);
  			BTScanPosUnpinIfPinned(so->currPos);
  		}
--- 585,629 ----
  	if (so->markItemIndex >= 0)
  	{
  		/*
! 		 * The scan has never moved to a new page since the last mark.  Just
  		 * restore the itemIndex.
+ 		 *
+ 		 * NB: In this case we can't count on anything in so->markPos to be
+ 		 * accurate.
  		 */
  		so->currPos.itemIndex = so->markItemIndex;
  	}
! 	else if (so->currPos.currPage == so->markPos.currPage)
  	{
  		/*
! 		 * so->markItemIndex < 0 but mark and current positions are on the
! 		 * same page.  This would be an unusual case, where the scan moved to
! 		 * a new index page after the mark, restored, and later restored again
! 		 * without moving off the marked page.  It is not clear that this code
! 		 * can currently be reached, but it seems better to make this function
! 		 * robust for this case than to Assert() or elog() that it can't
! 		 * happen.
  		 *
! 		 * We neither want to set so->markItemIndex >= 0 (because that could
! 		 * cause a later move to a new page to redo the memcpy() executions)
! 		 * nor re-execute the memcpy() functions for a restore within the same
! 		 * page.  The previous restore to this page already set everything
! 		 * except markPos as it should be.
! 		 */
! 		so->currPos.itemIndex = so->markPos.itemIndex;
! 	}
! 	else
! 	{
! 		/*
! 		 * The scan moved to a new page after last mark or restore, and we are
! 		 * now restoring to the marked page.  We aren't holding any read
! 		 * locks, but if we're still holding the pin for the current position,
! 		 * we must drop it.
  		 */
  		if (BTScanPosIsValid(so->currPos))
  		{
  			/* Before leaving current page, deal with any killed items */
! 			if (so->numKilled > 0)
  				_bt_killitems(scan);
  			BTScanPosUnpinIfPinned(so->currPos);
  		}