diff --git a/src/bin/e_widget_slider.c b/src/bin/e_widget_slider.c
index f83721aff..b46c5b148 100644
--- a/src/bin/e_widget_slider.c
+++ b/src/bin/e_widget_slider.c
@@ -19,7 +19,7 @@ static void _e_wid_disable_hook(Evas_Object *obj);
 
 /* externally accessible functions */
 EAPI Evas_Object *
-e_widget_slider_add(Evas *evas, int horiz, int rev, char *fmt, double min, double max, double step, int count, double *dval, int *ival, Evas_Coord size)
+e_widget_slider_add(Evas *evas, int horiz, int rev, const char *fmt, double min, double max, double step, int count, double *dval, int *ival, Evas_Coord size)
 {
    Evas_Object *obj, *o;
    E_Widget_Data *wd;
diff --git a/src/bin/e_widget_slider.h b/src/bin/e_widget_slider.h
index b212bdf48..e3e9941c0 100644
--- a/src/bin/e_widget_slider.h
+++ b/src/bin/e_widget_slider.h
@@ -6,7 +6,7 @@
 #ifndef E_WIDGET_SLIDER_H
 #define E_WIDGET_SLIDER_H
 
-EAPI Evas_Object *e_widget_slider_add(Evas *evas, int horiz, int rev, char *fmt, double min, double max, double step, int count, double *dval, int *ival, Evas_Coord size);
+EAPI Evas_Object *e_widget_slider_add(Evas *evas, int horiz, int rev, const char *fmt, double min, double max, double step, int count, double *dval, int *ival, Evas_Coord size);
 EAPI int e_widget_slider_value_double_set(Evas_Object *slider, double dval);
 EAPI int e_widget_slider_value_int_set(Evas_Object *slider, int ival);
 EAPI int e_widget_slider_value_double_get(Evas_Object *slider, double *dval);