diff --git a/gio/gtestdbus.c b/gio/gtestdbus.c
index 8c5de3355..9ff74e653 100644
--- a/gio/gtestdbus.c
+++ b/gio/gtestdbus.c
@@ -62,13 +62,12 @@ typedef struct
   gboolean   timed_out;
 } WeakNotifyData;
 
-static gboolean
+static void
 on_weak_notify_timeout (gpointer user_data)
 {
   WeakNotifyData *data = user_data;
   data->timed_out = TRUE;
   g_main_loop_quit (data->loop);
-  return FALSE;
 }
 
 static gboolean
@@ -95,7 +94,7 @@ _g_object_unref_and_wait_weak_notify (gpointer object)
   g_idle_add (unref_on_idle, object);
 
   /* Make sure we don't block forever */
-  timeout_id = g_timeout_add_seconds (30, on_weak_notify_timeout, &data);
+  timeout_id = g_timeout_add_seconds_once (30, on_weak_notify_timeout, &data);
 
   g_main_loop_run (data.loop);
 
diff --git a/gio/tests/file.c b/gio/tests/file.c
index ad2f945f9..754c6c326 100644
--- a/gio/tests/file.c
+++ b/gio/tests/file.c
@@ -452,15 +452,13 @@ created_cb (GObject      *source,
                                data);
 }
 
-static gboolean
+static void
 stop_timeout (gpointer user_data)
 {
   CreateDeleteData *data = user_data;
 
   data->timed_out = TRUE;
   g_main_context_wakeup (data->context);
-
-  return G_SOURCE_REMOVE;
 }
 
 /*
@@ -518,7 +516,7 @@ test_create_delete (gconstpointer d)
 
   /* Use the global default main context */
   data->context = NULL;
-  data->timeout = g_timeout_add_seconds (10, stop_timeout, data);
+  data->timeout = g_timeout_add_seconds_once (10, stop_timeout, data);
 
   g_file_create_async (data->file, 0, 0, NULL, created_cb, data);
 
diff --git a/gio/tests/gapplication.c b/gio/tests/gapplication.c
index 1a2600099..b0584eb5f 100644
--- a/gio/tests/gapplication.c
+++ b/gio/tests/gapplication.c
@@ -1117,15 +1117,13 @@ activate (gpointer data)
   /* GApplication complains if we don't connect to ::activate */
 }
 
-static gboolean
+static void
 quit_already (gpointer user_data)
 {
   TestReplaceData *data = user_data;
 
   g_application_quit (data->app);
   data->timeout_id = 0;
-
-  return G_SOURCE_REMOVE;
 }
 
 static void
@@ -1177,7 +1175,7 @@ test_replace (gconstpointer data)
       g_signal_connect (app, "activate", G_CALLBACK (activate), NULL);
 
       if (!allow)
-        data.timeout_id = g_timeout_add_seconds (1, quit_already, &data);
+        data.timeout_id = g_timeout_add_seconds_once (1, quit_already, &data);
 
       g_application_run (app, G_N_ELEMENTS (argv) - 1, argv);
 
diff --git a/gio/tests/gdbus-connection-slow.c b/gio/tests/gdbus-connection-slow.c
index 5a3479234..06f59493c 100644
--- a/gio/tests/gdbus-connection-slow.c
+++ b/gio/tests/gdbus-connection-slow.c
@@ -128,14 +128,12 @@ test_connection_flush (void)
 /* the test will fail if the service name has not appeared after this amount of seconds */
 #define LARGE_MESSAGE_TIMEOUT_SECONDS 10
 
-static gboolean
+static void
 large_message_timeout_cb (gpointer data)
 {
   (void)data;
 
   g_error ("Error: timeout waiting for dbus name to appear");
-
-  return G_SOURCE_REMOVE;
 }
 
 static void
@@ -200,9 +198,9 @@ test_connection_large_message (void)
   /* this is safe; testserver will exit once the bus goes away */
   g_assert (g_spawn_command_line_async (g_test_get_filename (G_TEST_BUILT, "gdbus-testserver", NULL), NULL));
 
-  timeout_id = g_timeout_add_seconds (LARGE_MESSAGE_TIMEOUT_SECONDS,
-                                      large_message_timeout_cb,
-                                      NULL);
+  timeout_id = g_timeout_add_seconds_once (LARGE_MESSAGE_TIMEOUT_SECONDS,
+                                           large_message_timeout_cb,
+                                           NULL);
 
   watcher_id = g_bus_watch_name (G_BUS_TYPE_SESSION,
                                  "com.example.TestService",
diff --git a/gio/tests/gmenumodel.c b/gio/tests/gmenumodel.c
index fb52b4c6d..d75f36a29 100644
--- a/gio/tests/gmenumodel.c
+++ b/gio/tests/gmenumodel.c
@@ -7,12 +7,10 @@
 
 #include "glib/glib-private.h"
 
-static gboolean
+static void
 time_out (gpointer unused G_GNUC_UNUSED)
 {
   g_error ("Timed out");
-  /* not reached */
-  return FALSE;
 }
 
 static guint
@@ -22,7 +20,7 @@ add_timeout (guint seconds)
   /* Safety-catch against the main loop having blocked */
   alarm (seconds + 5);
 #endif
-  return g_timeout_add_seconds (seconds, time_out, NULL);
+  return g_timeout_add_seconds_once (seconds, time_out, NULL);
 }
 
 static void
diff --git a/gio/tests/gsubprocess.c b/gio/tests/gsubprocess.c
index 515a11267..30947596e 100644
--- a/gio/tests/gsubprocess.c
+++ b/gio/tests/gsubprocess.c
@@ -1288,14 +1288,12 @@ test_communicate_utf8_invalid (void)
   g_object_unref (proc);
 }
 
-static gboolean
+static void
 send_terminate (gpointer   user_data)
 {
   GSubprocess *proc = user_data;
 
   g_subprocess_force_exit (proc);
-
-  return FALSE;
 }
 
 static void
@@ -1341,7 +1339,7 @@ test_terminate (void)
 
   g_subprocess_wait_async (proc, NULL, on_request_quit_exited, loop);
 
-  g_timeout_add_seconds (3, send_terminate, proc);
+  g_timeout_add_seconds_once (3, send_terminate, proc);
 
   g_main_loop_run (loop);
 
@@ -1350,14 +1348,12 @@ test_terminate (void)
 }
 
 #ifdef G_OS_UNIX
-static gboolean
+static void
 send_signal (gpointer user_data)
 {
   GSubprocess *proc = user_data;
 
   g_subprocess_send_signal (proc, SIGKILL);
-
-  return FALSE;
 }
 
 static void
@@ -1378,7 +1374,7 @@ test_signal (void)
 
   g_subprocess_wait_async (proc, NULL, on_request_quit_exited, loop);
 
-  g_timeout_add_seconds (3, send_signal, proc);
+  g_timeout_add_seconds_once (3, send_signal, proc);
 
   g_main_loop_run (loop);