diff --git a/include/villas/config_helper.h b/include/villas/config_helper.h
index af1be6658..14ce43145 100644
--- a/include/villas/config_helper.h
+++ b/include/villas/config_helper.h
@@ -43,7 +43,7 @@ int json_to_config(json_t *json, config_setting_t *parent);
 #endif /* LIBCONFIG_FOUND */
 
 /* Create a JSON object from command line parameters. */
-json_t *json_load_cli(int argc, char *argv[]);
+json_t *json_load_cli(int argc, const char *argv[]);
 
 int json_object_extend_str(json_t *orig, const char *str);
 
diff --git a/lib/config_helper.c b/lib/config_helper.c
index 9592da4bb..23b5590f7 100644
--- a/lib/config_helper.c
+++ b/lib/config_helper.c
@@ -248,12 +248,13 @@ success:
 		json_object_set(subobj, key1, new);
 }
 
-json_t * json_load_cli(int argc, char *argv[])
+json_t * json_load_cli(int argc, const char *argv[])
 {
-	char *opt;
-	char *key = NULL;
-	char *value = NULL;
-	char *sep, *cpy;
+	const char *opt;
+	const char *key = NULL;
+	const char *value = NULL;
+	const char *sep;
+	char *cpy;
 
 	json_t *json = json_object();