diff --git a/libguile/srfi-14.c b/libguile/srfi-14.c
index b266400ea..42ee85d57 100644
--- a/libguile/srfi-14.c
+++ b/libguile/srfi-14.c
@@ -2045,7 +2045,7 @@ SCM_DEFINE (scm_sys_char_set_dump, "%char-set-dump", 1, 0, 0, (SCM charset),
   SCM ranges = SCM_EOL, elt;
   size_t i;
   scm_t_char_set *cs;
-  char codepoint_string_lo[9], codepoint_string_hi[9];
+  char codepoint_string_lo[13], codepoint_string_hi[13];
 
   SCM_VALIDATE_SMOB (1, charset, charset);
   cs = SCM_CHARSET_DATA (charset);