compilation error using dos command

[Ben]

I'm using the dos command to compile our app web forms
dll via the following batch file :

set InDir=c:\test\
set OutDir=c:\inetpub\wwwroot\test\bin\
set InFile1=%InDir%Default.aspx.cs
set InFile2=%InDir%Login.aspx.cs
set OutFile=%OutDir%\test.webform.dll
set assemblies=System.dll,System.Data.dll,System.Web.dll,%
OutDir%test.biz.dll
csc /t:library /out:%OutFile% %InFile1% %InFile2% /r:%
assemblies%

It works fine until the no. of InFile grows to over 50
that it complains "The input line is too long."

Is there a way to resolve this?

Thanks,
Ben