diff --git a/subreader.c b/subreader.c
index 3fb29f29b2..4010424cdc 100644
--- a/subreader.c
+++ b/subreader.c
@@ -1270,7 +1270,7 @@ struct subreader {
 };
 
 #ifdef HAVE_ENCA
-const char* guess_buffer_cp(unsigned char* buffer, int buflen,  char *preferred_language, const char *fallback)
+const char* guess_buffer_cp(unsigned char* buffer, int buflen, const char *preferred_language, const char *fallback)
 {
     const char **languages;
     size_t langcnt;
@@ -1310,7 +1310,7 @@ const char* guess_buffer_cp(unsigned char* buffer, int buflen,  char *preferred_
 }
 
 #define MAX_GUESS_BUFFER_SIZE (256*1024)
-const char* guess_cp(stream_t *st, char *preferred_language, const char *fallback)
+const char* guess_cp(stream_t *st, const char *preferred_language, const char *fallback)
 {
     size_t buflen;
     unsigned char *buffer;
diff --git a/subreader.h b/subreader.h
index ae12c4dc5c..c6c18dc550 100644
--- a/subreader.h
+++ b/subreader.h
@@ -74,8 +74,8 @@ struct stream_st;
 void subcp_open (struct stream_st *st); /* for demux_ogg.c */
 void subcp_close (void); /* for demux_ogg.c */
 #ifdef HAVE_ENCA
-const char* guess_buffer_cp(unsigned char* buffer, int buflen, char *preferred_language, const char *fallback);
-const char* guess_cp(struct stream_st *st, char *preferred_language, const char *fallback);
+const char* guess_buffer_cp(unsigned char* buffer, int buflen, const char *preferred_language, const char *fallback);
+const char* guess_cp(struct stream_st *st, const char *preferred_language, const char *fallback);
 #endif
 char ** sub_filenames(const char *path, char *fname);
 void list_sub_file(sub_data* subd);