diff --git a/src/mustach-dhcpd-pools.c b/src/mustach-dhcpd-pools.c
index 54a2009..90e09e5 100644
--- a/src/mustach-dhcpd-pools.c
+++ b/src/mustach-dhcpd-pools.c
@@ -276,6 +276,8 @@ static char *must_read_template(const char *filename)
 	struct stat s;
 	char *result;
 
+	if (filename == NULL)
+		error(EXIT_FAILURE, 0, "must_read_template: --mustach argument missing");
 	if ((f = open(filename, O_RDONLY)) < 0) {
 		error(EXIT_FAILURE, errno, "must_read_template: open: %s", filename);
 	}