diff --git a/docs/cookbook/c/clean.do b/docs/cookbook/c/clean.do
new file mode 100644
index 0000000..4b7488c
--- /dev/null
+++ b/docs/cookbook/c/clean.do
@@ -0,0 +1,2 @@
+rm -rf out out.*
+rm -f *~ .*~ */*~ */.*~ sources arches allconfig when.c
diff --git a/docs/cookbook/c/rc/posix.rc.od b/docs/cookbook/c/rc/posix.rc.od
index 546fc8a..4a6b172 100644
--- a/docs/cookbook/c/rc/posix.rc.od
+++ b/docs/cookbook/c/rc/posix.rc.od
@@ -8,9 +8,13 @@ struct timespec x;
 '
 
 x=
+rc_replaceln HAS_POSIX 1
 if ! rc_compile cc link "$prog"; then
-    x="-D_XOPEN_SOURCE=500"
-    rc_appendln CPPFLAGS "$x"
-    rc_compile cc link "$prog"
+	x="-D_XOPEN_SOURCE=500"
+	rc_appendln CPPFLAGS "$x"
+	if ! rc_compile cc link "$prog"; then
+		rc_undo
+		rc_replaceln HAS_POSIX ""
+	fi
 fi
 rc_save
diff --git a/redoconf/rc.sh b/redoconf/rc.sh
index bc2fa4d..2163a15 100644
--- a/redoconf/rc.sh
+++ b/redoconf/rc.sh
@@ -15,7 +15,7 @@ _rc_exit_check() {
 		echo "Fatal: used redoconf/rc.sh but didn't call rc_include." >&2
 		exit 91
 	elif [ -n "$RC_QUEUE" ]; then
-		echo "Fatal: must call rc_save or rc_undo before ending." >&2
+		echo "Fatal: script exited without rc_save or rc_undo." >&2
 		exit 92
 	fi
 }