diff --git a/common/draw.c b/common/draw.c
index 76e72ccce..3fc4b766b 100644
--- a/common/draw.c
+++ b/common/draw.c
@@ -753,7 +753,7 @@ draw_rotate(DrawCtx *ctx, Drawable dest, int dest_w, int dest_h,
  * \return text width
  */
 unsigned short
-draw_textwidth(Display *disp, font_t *font, char *text)
+draw_textwidth(Display *disp, font_t *font, const char *text)
 {
     cairo_surface_t *surface;
     cairo_t *cr;
diff --git a/common/draw.h b/common/draw.h
index 63b902825..969b3933c 100644
--- a/common/draw.h
+++ b/common/draw.h
@@ -135,7 +135,7 @@ void draw_image(DrawCtx *, int, int, int, const char *);
 void draw_image_from_argb_data(DrawCtx *, int, int, int, int, int, unsigned char *);
 area_t draw_get_image_size(const char *filename);
 void draw_rotate(DrawCtx *, Drawable, int, int, double, int, int);
-unsigned short draw_textwidth(Display *, font_t *, char *);
+unsigned short draw_textwidth(Display *, font_t *, const char *);
 Alignment draw_align_get_from_str(const char *);
 Bool draw_color_new(Display *, int, const char *, XColor *);
 void draw_style_init(Display *, int, cfg_t *, style_t *, style_t *);