diff --git a/spa/plugins/bluez5/modemmanager.c b/spa/plugins/bluez5/modemmanager.c
index c4ee77611..bc740acc6 100644
--- a/spa/plugins/bluez5/modemmanager.c
+++ b/spa/plugins/bluez5/modemmanager.c
@@ -771,7 +771,7 @@ bool mm_is_available(void *modemmanager)
 	return this->modem.path != NULL;
 }
 
-unsigned int mm_supported_features()
+unsigned int mm_supported_features(void)
 {
 	return SPA_BT_HFP_AG_FEATURE_REJECT_CALL | SPA_BT_HFP_AG_FEATURE_ENHANCED_CALL_STATUS;
 }
diff --git a/spa/plugins/bluez5/modemmanager.h b/spa/plugins/bluez5/modemmanager.h
index f21db94f5..09bd65524 100644
--- a/spa/plugins/bluez5/modemmanager.h
+++ b/spa/plugins/bluez5/modemmanager.h
@@ -71,7 +71,7 @@ void *mm_register(struct spa_log *log, void *dbus_connection, const struct spa_d
                   const struct mm_ops *ops, void *user_data);
 void mm_unregister(void *data);
 bool mm_is_available(void *modemmanager);
-unsigned int mm_supported_features();
+unsigned int mm_supported_features(void);
 bool mm_answer_call(void *modemmanager, void *user_data, enum cmee_error *error);
 bool mm_hangup_call(void *modemmanager, void *user_data, enum cmee_error *error);
 bool mm_do_call(void *modemmanager, const char* number, void *user_data, enum cmee_error *error);