diff --git a/src/conio/bitmap_con.c b/src/conio/bitmap_con.c
index ba5e67e1c00ac0854ab750c028172868d9d0ed82..06fabef73291b7ecced287fa04b72784f042c4ab 100644
--- a/src/conio/bitmap_con.c
+++ b/src/conio/bitmap_con.c
@@ -104,7 +104,7 @@ pthread_mutex_t blinker_lock;
 
 /* Forward declarations */
 
-static int bitmap_loadfont_locked(char *filename);
+static int bitmap_loadfont_locked(const char *filename);
 static void set_vmem_cell(struct vstat_vmem *vmem_ptr, size_t pos, uint16_t cell, uint32_t fg, uint32_t bg);
 static int bitmap_attr2palette_locked(uint8_t attr, uint32_t *fgp, uint32_t *bgp);
 static void	cb_drawrect(struct rectlist *data);
@@ -125,7 +125,7 @@ void bitmap_drv_free_rect(struct rectlist *rect);
 /* These functions get called from the driver and ciolib only */
 /**************************************************************/
 
-static int bitmap_loadfont_locked(char *filename)
+static int bitmap_loadfont_locked(const char *filename)
 {
 	static char current_filename[MAX_PATH];
 	unsigned int fontsize;
@@ -1108,7 +1108,7 @@ int bitmap_getfont(int font_num)
 	return ret;
 }
 
-int bitmap_loadfont(char *filename)
+int bitmap_loadfont(const char *filename)
 {
 	int ret;
 
diff --git a/src/conio/bitmap_con.h b/src/conio/bitmap_con.h
index e268f66bd080db325f9d8c879471788664d6fd5e..e6879832f581ff285a4302d17505e6fc7dc84442 100644
--- a/src/conio/bitmap_con.h
+++ b/src/conio/bitmap_con.h
@@ -30,7 +30,7 @@ void bitmap_gotoxy(int x, int y);
 void bitmap_setcursortype(int type);
 int bitmap_setfont(int font, int force, int font_no);
 int bitmap_getfont(int fnum);
-int bitmap_loadfont(char *filename);
+int bitmap_loadfont(const char *filename);
 int bitmap_movetext(int x, int y, int ex, int ey, int tox, int toy);
 void bitmap_clreol(void);
 void bitmap_clrscr(void);
diff --git a/src/conio/ciolib.c b/src/conio/ciolib.c
index a1bd3c2a1ded30ee6d618be95c440584267949f8..7742eb2ef2b7a49b1139cec7eed442b1cf7feea7 100644
--- a/src/conio/ciolib.c
+++ b/src/conio/ciolib.c
@@ -1489,7 +1489,7 @@ CIOLIBEXPORT int ciolib_getfont(int font_num)
 
 /* Optional */
 /* Return Non-zero on success */
-CIOLIBEXPORT int ciolib_loadfont(char *filename)
+CIOLIBEXPORT int ciolib_loadfont(const char *filename)
 {
 	CIOLIB_INIT();
 
diff --git a/src/conio/ciolib.h b/src/conio/ciolib.h
index b13c2c95baf7d6132a4c5952d9f4aff2d01a6538..ba56dfdc91700ed59eef3fc0276d44f58fc6a225 100644
--- a/src/conio/ciolib.h
+++ b/src/conio/ciolib.h
@@ -363,7 +363,7 @@ typedef struct {
 	void	(*resume)		(void);
 	int		(*setfont)		(int font, int force, int font_num);
 	int		(*getfont)		(int font_num);
-	int		(*loadfont)		(char *filename);
+	int		(*loadfont)		(const char *filename);
 	int		(*get_window_info)		(int* width, int* height, int* xpos, int* ypos);
 	void	(*getcustomcursor)	(int *startline, int *endline, int *range, int *blink, int *visible);
 	void	(*setcustomcursor)	(int startline, int endline, int range, int blink, int visible);
@@ -448,7 +448,7 @@ CIOLIBEXPORT void ciolib_copytext(const char *text, size_t buflen);
 CIOLIBEXPORT char * ciolib_getcliptext(void);
 CIOLIBEXPORT int ciolib_setfont(int font, int force, int font_num);
 CIOLIBEXPORT int ciolib_getfont(int font_num);
-CIOLIBEXPORT int ciolib_loadfont(char *filename);
+CIOLIBEXPORT int ciolib_loadfont(const char *filename);
 CIOLIBEXPORT int ciolib_get_window_info(int *width, int *height, int *xpos, int *ypos);
 CIOLIBEXPORT void ciolib_beep(void);
 CIOLIBEXPORT void ciolib_getcustomcursor(int *startline, int *endline, int *range, int *blink, int *visible);
diff --git a/src/conio/sdl_con.h b/src/conio/sdl_con.h
index 8484f8a6160dc35b0c29658dd21d3110fbc5ae97..000bbf4942de8617a576833ebed47ca67631eff1 100644
--- a/src/conio/sdl_con.h
+++ b/src/conio/sdl_con.h
@@ -32,7 +32,7 @@ void sdl_copytext(const char *text, size_t buflen);
 char *sdl_getcliptext(void);
 int sdl_setfont(int font, int force);
 int sdl_getfont(void);
-int sdl_loadfont(char *filename);
+int sdl_loadfont(const char *filename);
 int sdl_get_window_info(int *width, int *height, int *xpos, int *ypos);
 int sdl_setpalette(uint32_t index, uint16_t r, uint16_t g, uint16_t b);
 void sdl_setwinsize(int w, int h);
diff --git a/src/conio/x_cio.h b/src/conio/x_cio.h
index 158d052d33f59fd9de8aeb056e5cabe3afd26eaf..95dade74705fbd2f2d250b95a7b4934e08b02ed1 100644
--- a/src/conio/x_cio.h
+++ b/src/conio/x_cio.h
@@ -69,7 +69,7 @@ void x_copytext(const char *text, size_t buflen);
 char *x_getcliptext(void);
 int x_setfont(int font, int force);
 int x_getfont(void);
-int x_loadfont(char *filename);
+int x_loadfont(const char *filename);
 int x_get_window_info(int *width, int *height, int *xpos, int *ypos);
 void x11_drawrect(struct rectlist *data);
 void x11_flush(void);