--- configure.ac.orig	2018-01-20 15:44:37 UTC
+++ configure.ac
@@ -20,8 +20,13 @@ AC_PATH_PROG(CSC, csc, no)
 AC_PATH_PROG(GMCS, gmcs, no)
 AC_PATH_PROG(MCS, mcs, no)
 AC_PATH_PROG(RUNTIME, mono, no)
+AC_PATH_PROG(SN, sn, no)
 CS="C#"
 
+if test "x$SN" = "xno" ; then
+	AC_MSG_ERROR([No key signing tool found])
+fi
+
 if test "x$CSC" = "xno" ; then
 	if test "x$GMCS" = "xno" ; then
 		if test "x$MCS" = "xno" ; then