--- rxvt-unicode/autogen.sh	2017/10/13 17:13:40	1.3
+++ rxvt-unicode/autogen.sh	2017/10/13 17:13:48	1.4
@@ -12,6 +12,18 @@
    exit 1
 fi
 
+if ! [ -e libptytty/ptytty.m4 ]; then
+   cat <<EOF
+**
+** libptytty/ directory is missing
+**
+** you need a checkout of libptytty (http://software.schmorp.de/pkg/libptytty.html)
+** in the top-level build directory.
+**
+EOF
+   exit 1
+fi
+
 if autoheader && autoconf; then
 	rm -rf autom4te.cache
 	echo "Now run ./configure"