diff --git a/Makefile b/Makefile
index d6af126bb1..a8de0c6558 100644
--- a/Makefile
+++ b/Makefile
@@ -39,7 +39,7 @@
 #
 SDK         ?=
 CSC         = mcs $(SDK)
-CSFLAGS     = -nologo -warn:4 -codepage:utf8 -unsafe -warnaserror
+CSFLAGS     = -nologo -warn:4 -codepage:utf8 -langversion:5 -unsafe -warnaserror
 DEFINE      = TRACE
 COMMON_LIBS = System.dll System.Core.dll System.Data.dll System.Data.DataSetExtensions.dll System.Drawing.dll System.Xml.dll thirdparty/download/ICSharpCode.SharpZipLib.dll thirdparty/download/FuzzyLogicLibrary.dll thirdparty/download/MaxMind.Db.dll thirdparty/download/Eluant.dll thirdparty/download/SmarIrc4net.dll thirdparty/download/rix0rrr.BeaconLib.dll
 NUNIT_LIBS_PATH :=