diff --git a/src/dbus.c b/src/dbus.c
index b719217c..01d43cf4 100644
--- a/src/dbus.c
+++ b/src/dbus.c
@@ -415,7 +415,7 @@ gboolean __ofono_dbus_valid_object_path(const char *path)
 	return TRUE;
 }
 
-DBusConnection *ofono_dbus_get_connection()
+DBusConnection *ofono_dbus_get_connection(void)
 {
 	return g_connection;
 }
diff --git a/src/main.c b/src/main.c
index 87fb0ab8..3db88198 100644
--- a/src/main.c
+++ b/src/main.c
@@ -42,7 +42,7 @@
 
 static GMainLoop *event_loop;
 
-void __ofono_exit()
+void __ofono_exit(void)
 {
 	g_main_loop_quit(event_loop);
 }
diff --git a/src/manager.c b/src/manager.c
index 0649bcc3..70759091 100644
--- a/src/manager.c
+++ b/src/manager.c
@@ -91,7 +91,7 @@ static GDBusSignalTable manager_signals[] = {
 	{ }
 };
 
-int __ofono_manager_init()
+int __ofono_manager_init(void)
 {
 	DBusConnection *conn = ofono_dbus_get_connection();
 	gboolean ret;
@@ -107,7 +107,7 @@ int __ofono_manager_init()
 	return 0;
 }
 
-void __ofono_manager_cleanup()
+void __ofono_manager_cleanup(void)
 {
 	DBusConnection *conn = ofono_dbus_get_connection();
 
diff --git a/src/modem.c b/src/modem.c
index 953d6c31..981aabc2 100644
--- a/src/modem.c
+++ b/src/modem.c
@@ -1560,12 +1560,12 @@ static void sim_watch(struct ofono_atom *atom,
 							modem, NULL);
 }
 
-void __ofono_modemwatch_init()
+void __ofono_modemwatch_init(void)
 {
 	g_modemwatches = __ofono_watchlist_new(g_free);
 }
 
-void __ofono_modemwatch_cleanup()
+void __ofono_modemwatch_cleanup(void)
 {
 	__ofono_watchlist_free(g_modemwatches);
 }
@@ -1850,7 +1850,7 @@ void ofono_modem_driver_unregister(const struct ofono_modem_driver *d)
 	}
 }
 
-void __ofono_modem_shutdown()
+void __ofono_modem_shutdown(void)
 {
 	struct ofono_modem *modem;
 	GSList *l;
diff --git a/src/ofono.h b/src/ofono.h
index cab70cdc..77567c2d 100644
--- a/src/ofono.h
+++ b/src/ofono.h
@@ -25,12 +25,12 @@
 
 #include <ofono/types.h>
 
-void __ofono_exit();
+void __ofono_exit(void);
 
-int __ofono_manager_init();
-void __ofono_manager_cleanup();
+int __ofono_manager_init(void);
+void __ofono_manager_cleanup(void);
 
-void __ofono_modem_shutdown();
+void __ofono_modem_shutdown(void);
 
 #include <ofono/log.h>
 
@@ -174,8 +174,8 @@ void __ofono_atom_free(struct ofono_atom *atom);
 
 typedef void (*ofono_modemwatch_cb_t)(struct ofono_modem *modem,
 					gboolean added, void *data);
-void __ofono_modemwatch_init();
-void __ofono_modemwatch_cleanup();
+void __ofono_modemwatch_init(void);
+void __ofono_modemwatch_cleanup(void);
 unsigned int __ofono_modemwatch_add(ofono_modemwatch_cb_t cb, void *user,
 					ofono_destroy_func destroy);
 gboolean __ofono_modemwatch_remove(unsigned int id);