diff --git a/src/intl/charsets.c b/src/intl/charsets.c
index b9f69bdc..50c51c46 100644
--- a/src/intl/charsets.c
+++ b/src/intl/charsets.c
@@ -724,7 +724,7 @@ flush:
 
 #ifndef USE_FASTFIND
 int
-get_cp_index(unsigned char *name)
+get_cp_index(const unsigned char *name)
 {
 	int i, a;
 	int syscp = 0;
@@ -805,7 +805,7 @@ static struct fastfind_index ff_charsets_index
 /* It searchs for a charset named @name or one of its aliases and
  * returns index for it or -1 if not found. */
 int
-get_cp_index(unsigned char *name)
+get_cp_index(const unsigned char *name)
 {
 	struct codepage_desc *codepage;
 	int syscp = 0;
diff --git a/src/intl/charsets.h b/src/intl/charsets.h
index 91daffec..8c2549d9 100644
--- a/src/intl/charsets.h
+++ b/src/intl/charsets.h
@@ -54,7 +54,7 @@ unsigned char *convert_string(struct conv_table *convert_table,
 			      void (*callback)(void *data, unsigned char *buf, int buflen),
 			      void *callback_data);
 
-int get_cp_index(unsigned char *);
+int get_cp_index(const unsigned char *);
 unsigned char *get_cp_name(int);
 unsigned char *get_cp_mime_name(int);
 int is_cp_special(int);