diff --git a/src/conio/scale.c b/src/conio/scale.c
index afddfa3a2acdb14d1ae8f80d141241e7eaa5c927..db12e77395bed7f2fde9fdb93d78fd187fd18b6a 100644
--- a/src/conio/scale.c
+++ b/src/conio/scale.c
@@ -763,7 +763,7 @@ struct YCoCg_data {
 };
 
 static inline void
-RGB_to_YCoCg(const uint32_t RGB, struct YCoCg_data *YCoCg)
+RGB_to_YCoCg(const uint32_t RGB, struct YCoCg_data * const YCoCg)
 {
 	signed R, G, B, tmp;
 
@@ -778,7 +778,7 @@ RGB_to_YCoCg(const uint32_t RGB, struct YCoCg_data *YCoCg)
 }
 
 static inline uint32_t
-YCoCg_to_RGB(struct YCoCg_data *YCoCg)
+YCoCg_to_RGB(struct YCoCg_data const * const YCoCg)
 {
 	signed Ri, Gi, Bi, tmp;
 	unsigned R, G, B;