diff --git a/Makefile b/Makefile
index b9e8bb7a8e..a438498c79 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
 CSC         = gmcs
-CSFLAGS     = -nologo -warn:4 -debug:full -optimize- -codepage:utf8 -unsafe
+CSFLAGS     = -nologo -warn:4 -debug:full -optimize- -codepage:utf8 -unsafe -warnaserror
 DEFINE      = DEBUG;TRACE
 COMMON_LIBS	= System.dll System.Core.dll System.Drawing.dll System.Xml.dll thirdparty/ICSharpCode.SharpZipLib.dll
 PHONY		= core tools package all mods clean distclean