--- a/incdefs.sh
+++ b/incdefs.sh
@@ -27,7 +27,7 @@
 	printf " -D_GNU_SOURCE"
 
 	# Get list of directories searched for header files.
-	dirs=$(${CC} -E -Wp,-v -xc /dev/null 2>&1 >/dev/null | grep ^" /")
+	dirs=$(echo "" | ${CPP} -Wp,-v - 2>&1 >/dev/null | grep ^" /")
 
 	# Look for clock_adjtime().
 	for d in $dirs; do