diff --git a/include/c64/vic.c b/include/c64/vic.c
index 28d6827..43894a1 100644
--- a/include/c64/vic.c
+++ b/include/c64/vic.c
@@ -21,7 +21,7 @@ int vic_sprgetx(byte s)
 	return vic.spr_pos[s].x | ((vic.spr_msbx & (1 << s)) ? 256 : 0);
 }
 
-void vic_setmode(VicMode mode, char * text, char * font)
+void vic_setmode(VicMode mode, const char * text, const char * font)
 {
 	switch (mode)
 	{
diff --git a/include/c64/vic.h b/include/c64/vic.h
index 718ae88..430de53 100644
--- a/include/c64/vic.h
+++ b/include/c64/vic.h
@@ -91,7 +91,7 @@ enum VicMode
 
 // set the display mode and base address. This will also
 // adapt the bank.
-void vic_setmode(VicMode mode, char * text, char * font);
+void vic_setmode(VicMode mode, const char * text, const char * font);
 
 // put a sprite at the given x/y location, taking care of the
 // x MSB