diff -uNr b/src/backend/commands/tablecmds.c a/src/backend/commands/tablecmds.c
--- b/src/backend/commands/tablecmds.c	2013-08-31 17:11:00.529744869 +0800
+++ a/src/backend/commands/tablecmds.c	2013-09-04 11:20:28.797652760 +0800
@@ -367,7 +367,7 @@
 					  AlteredTableInfo *tab, Relation rel,
 					  bool recurse, bool recursing,
 					  AlterTableCmd *cmd, LOCKMODE lockmode);
-static bool ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno);
+static bool ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno, int32 oldtypemod, int32 newtypemod);
 static void ATExecAlterColumnType(AlteredTableInfo *tab, Relation rel,
 					  AlterTableCmd *cmd, LOCKMODE lockmode);
 static void ATExecAlterColumnGenericOptions(Relation rel, const char *colName,
@@ -7480,7 +7480,7 @@
 		newval->expr = (Expr *) transform;
 
 		tab->newvals = lappend(tab->newvals, newval);
-		if (ATColumnChangeRequiresRewrite(transform, attnum))
+		if (ATColumnChangeRequiresRewrite(transform, attnum, attTup->atttypmod, targettypmod))
 			tab->rewrite = true;
 	}
 	else if (transform)
@@ -7530,7 +7530,7 @@
  * try to do that.
  */
 static bool
-ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno)
+ATColumnChangeRequiresRewrite(Node *expr, AttrNumber varattno, int32 oldtypemod, int32 newtypemod)
 {
 	Assert(expr != NULL);
 
@@ -7549,6 +7549,18 @@
 				return true;
 			expr = (Node *) d->arg;
 		}
+		else if (IsA(expr, FuncExpr))
+		{
+			int32	between = 0;
+
+			if(((FuncExpr *) expr)->funcresulttype == 1700 && ((FuncExpr *) expr)->funcid == 1703)
+				between = newtypemod - oldtypemod;
+
+			if(between > 0 && between < 1001)
+				return false;
+			else
+				return true;
+		}
 		else
 			return true;
 	}