diff --git a/glib/gdataset.c b/glib/gdataset.c
index 39806da4d..452c48730 100644
--- a/glib/gdataset.c
+++ b/glib/gdataset.c
@@ -935,7 +935,8 @@ g_datalist_id_get_data (GData  **datalist,
  * g_datalist_id_dup_data: (skip)
  * @datalist: location of a datalist
  * @key_id: the #GQuark identifying a data element
- * @dup_func: (scope call) (closure user_data): function to duplicate the old value
+ * @dup_func: (scope call) (closure user_data) (nullable): function to
+ *   duplicate the old value
  * @user_data: passed as user_data to @dup_func
  *
  * This is a variant of g_datalist_id_get_data() which
diff --git a/glib/gspawn.c b/glib/gspawn.c
index 112be3a32..3e2e6cf49 100644
--- a/glib/gspawn.c
+++ b/glib/gspawn.c
@@ -218,7 +218,8 @@ G_DEFINE_QUARK (g-spawn-exit-error-quark, g_spawn_exit_error)
  * @envp: (array zero-terminated=1) (element-type filename) (nullable):
  *     child's environment, or %NULL to inherit parent's
  * @flags: flags from #GSpawnFlags
- * @child_setup: (scope async): function to run in the child just before exec()
+ * @child_setup: (scope async) (closure user_data) (nullable): function to run
+ *     in the child just before `exec()`
  * @user_data: user data for @child_setup
  * @child_pid: (out) (optional): return location for child process reference, or %NULL
  * @error: return location for error
@@ -332,7 +333,8 @@ read_data (GString *str,
  * @envp: (array zero-terminated=1) (element-type filename) (nullable):
  *     child's environment, or %NULL to inherit parent's
  * @flags: flags from #GSpawnFlags
- * @child_setup: (scope async): function to run in the child just before exec()
+ * @child_setup: (scope call) (closure user_data) (nullable): function to run
+ *     in the child just before `exec()`
  * @user_data: user data for @child_setup
  * @standard_output: (out) (array zero-terminated=1) (element-type guint8) (optional): return location for child output, or %NULL
  * @standard_error: (out) (array zero-terminated=1) (element-type guint8) (optional): return location for child error messages, or %NULL
@@ -593,7 +595,8 @@ g_spawn_sync (const gchar          *working_directory,
  *     child's environment, or %NULL to inherit parent's, in the GLib file
  *     name encoding
  * @flags: flags from #GSpawnFlags
- * @child_setup: (scope async): function to run in the child just before exec()
+ * @child_setup: (scope async) (closure user_data) (nullable): function to run
+ *     in the child just before `exec()`
  * @user_data: user data for @child_setup
  * @child_pid: (out) (optional): return location for child process ID, or %NULL
  * @standard_input: (out) (optional): return location for file descriptor to write to child's stdin, or %NULL
@@ -643,7 +646,8 @@ g_spawn_async_with_pipes (const gchar          *working_directory,
  *     child's environment, or %NULL to inherit parent's, in the GLib file
  *     name encoding
  * @flags: flags from #GSpawnFlags
- * @child_setup: (scope async) (closure user_data): function to run in the child just before `exec()`
+ * @child_setup: (scope async) (closure user_data) (nullable): function to run
+ *     in the child just before `exec()`
  * @user_data: user data for @child_setup
  * @stdin_fd: file descriptor to use for child's stdin, or `-1`
  * @stdout_fd: file descriptor to use for child's stdout, or `-1`
@@ -929,7 +933,8 @@ g_spawn_async_with_pipes_and_fds (const gchar           *working_directory,
  *   it must be non-empty and %NULL-terminated
  * @envp: (array zero-terminated=1) (nullable): child's environment, or %NULL to inherit parent's, in the GLib file name encoding
  * @flags: flags from #GSpawnFlags
- * @child_setup: (scope async) (closure user_data): function to run in the child just before exec()
+ * @child_setup: (scope async) (closure user_data) (nullable): function to run
+ *   in the child just before `exec()`
  * @user_data: user data for @child_setup
  * @child_pid: (out) (optional): return location for child process ID, or %NULL
  * @stdin_fd: file descriptor to use for child's stdin, or `-1`