diff --git a/gtk/gtkprivate.h b/gtk/gtkprivate.h
index af130cd3f0..1c74f62853 100644
--- a/gtk/gtkprivate.h
+++ b/gtk/gtkprivate.h
@@ -92,7 +92,7 @@ gboolean        _gtk_propagate_captured_event  (GtkWidget       *widget,
                                                 GtkWidget       *topmost);
 
 
-gdouble _gtk_get_slowdown ();
+gdouble _gtk_get_slowdown (void);
 void    _gtk_set_slowdown (gdouble slowdown_factor);
 
 gboolean gtk_should_use_portal (void);
diff --git a/gtk/gtkprogresstracker.c b/gtk/gtkprogresstracker.c
index c1d3f44215..81cca35d19 100644
--- a/gtk/gtkprogresstracker.c
+++ b/gtk/gtkprogresstracker.c
@@ -45,7 +45,7 @@ _gtk_set_slowdown (gdouble factor)
 }
 
 gdouble
-_gtk_get_slowdown (gdouble factor)
+_gtk_get_slowdown (void)
 {
   return gtk_slowdown;
 }