diff --git a/libguile/chars.h b/libguile/chars.h
index 7c1152d72..cb0ee49e2 100644
--- a/libguile/chars.h
+++ b/libguile/chars.h
@@ -55,9 +55,9 @@
 
 
 
-extern char *scm_charnames[];
+extern char *const scm_charnames[];
 extern int scm_n_charnames;
-extern char scm_charnums[];
+extern const char scm_charnums[];