diff --git a/src/strutil.c b/src/strutil.c
index 379a9632d..5b66f2f12 100644
--- a/src/strutil.c
+++ b/src/strutil.c
@@ -98,7 +98,7 @@ str_close_conv (GIConv conv)
 }
 
 static estr_t
-_str_convert (GIConv coder, char *string, int size, GString * buffer)
+_str_convert (GIConv coder, const char *string, int size, GString * buffer)
 {
     estr_t state  = ESTR_SUCCESS;
     gchar *tmp_buff = NULL;
@@ -234,19 +234,19 @@ _str_convert (GIConv coder, char *string, int size, GString * buffer)
 }
 
 estr_t
-str_convert (GIConv coder, char *string, GString * buffer)
+str_convert (GIConv coder, const char *string, GString * buffer)
 {
     return _str_convert (coder, string, -1, buffer);
 }
 
 estr_t
-str_nconvert (GIConv coder, char *string, int size, GString * buffer)
+str_nconvert (GIConv coder, const char *string, int size, GString * buffer)
 {
     return _str_convert (coder, string, size, buffer);
 }
 
 estr_t
-str_vfs_convert_from (GIConv coder, char *string, GString * buffer)
+str_vfs_convert_from (GIConv coder, const char *string, GString * buffer)
 {
     estr_t result;
 
diff --git a/src/strutil.h b/src/strutil.h
index c1c5fce9c..2efd49cf5 100644
--- a/src/strutil.h
+++ b/src/strutil.h
@@ -159,16 +159,16 @@ void str_close_conv (GIConv);
  * return 0 if there was no problem. 
  * otherwise return  ESTR_PROBLEM or ESTR_FAILURE
  */ 
-estr_t str_convert (GIConv, char *, GString *);
+estr_t str_convert (GIConv, const char *, GString *);
 
-estr_t str_nconvert (GIConv, char *, int, GString *);
+estr_t str_nconvert (GIConv, const char *, int, GString *);
 
 /* return only 0 or ESTR_FAILURE, because vfs must be able to convert result to
  * original string. (so no replace with questionmark)
  * if coder is str_cnv_from_term or str_cnv_not_convert, string is only copied,
  * so is possible to show file, that is not valid in terminal encoding
  */
-estr_t str_vfs_convert_from (GIConv, char *, GString *);
+estr_t str_vfs_convert_from (GIConv, const char *, GString *);
 
 /* if coder is str_cnv_to_term or str_cnv_not_convert, string is only copied,
  * does replace with questionmark