diff --git c/lib/regcomp.c i/lib/regcomp.c
index 6472ff6..665b2ab 100644
--- c/lib/regcomp.c
+++ i/lib/regcomp.c
@@ -18,6 +18,8 @@
    with this program; if not, write to the Free Software Foundation,
    Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA. */

+#include "intprops.h"
+#include "verify.h"
 static reg_errcode_t re_compile_internal (regex_t *preg, const char * pattern,
 					  size_t length, reg_syntax_t syntax);
 static void re_compile_fastmap_iter (regex_t *bufp,
@@ -541,7 +543,7 @@ regerror (errcode, preg, errbuf, errbuf_size)
     size_t errbuf_size;
 #else /* size_t might promote */
 size_t
-regerror (int errcode, const regex_t *_Restrict_ preg,
+regerror (int errcode, const regex_t *_Restrict_ preg _UNUSED_PARAMETER_,
 	  char *_Restrict_ errbuf, size_t errbuf_size)
 #endif
 {
@@ -1375,7 +1377,7 @@ calc_first (void *extra, bin_tree_t *node)

 /* Pass 2: compute NEXT on the tree.  Preorder visit.  */
 static reg_errcode_t
-calc_next (void *extra, bin_tree_t *node)
+calc_next (void *extra _UNUSED_PARAMETER_, bin_tree_t *node)
 {
   switch (node->token.type)
     {
@@ -2571,7 +2573,8 @@ parse_dup_op (bin_tree_t *elem, re_string_t *regexp, re_dfa_t *dfa,
   /* This loop is actually executed only when end != REG_MISSING,
      to rewrite <re>{0,n} as (<re>(<re>...<re>?)?)?...  We have
      already created the start+1-th copy.  */
-  if ((Idx) -1 < 0 || end != REG_MISSING)
+  verify (! TYPE_SIGNED (Idx));
+  if (end != REG_MISSING)
     for (i = start + 2; i <= end; ++i)
       {
 	elem = duplicate_tree (elem, dfa);
@@ -2731,7 +2734,8 @@ static reg_errcode_t
 internal_function
 build_collating_symbol (bitset_t sbcset,
 # ifdef RE_ENABLE_I18N
-			re_charset_t *mbcset, Idx *coll_sym_alloc,
+			re_charset_t *mbcset _UNUSED_PARAMETER_,
+			Idx *coll_sym_alloc _UNUSED_PARAMETER_,
 # endif
 			const unsigned char *name)
 {
@@ -3309,7 +3313,8 @@ parse_bracket_exp (re_string_t *regexp, re_dfa_t *dfa, re_token_t *token,

 static reg_errcode_t
 parse_bracket_element (bracket_elem_t *elem, re_string_t *regexp,
-		       re_token_t *token, int token_len, re_dfa_t *dfa,
+		       re_token_t *token, int token_len,
+		       re_dfa_t *dfa _UNUSED_PARAMETER_,
 		       reg_syntax_t syntax, bool accept_hyphen)
 {
 #ifdef RE_ENABLE_I18N
@@ -3396,8 +3401,9 @@ parse_bracket_symbol (bracket_elem_t *elem, re_string_t *regexp,

 static reg_errcode_t
 #ifdef RE_ENABLE_I18N
-build_equiv_class (bitset_t sbcset, re_charset_t *mbcset,
-		   Idx *equiv_class_alloc, const unsigned char *name)
+build_equiv_class (bitset_t sbcset, re_charset_t *mbcset _UNUSED_PARAMETER_,
+		   Idx *equiv_class_alloc _UNUSED_PARAMETER_,
+		   const unsigned char *name)
 #else /* not RE_ENABLE_I18N */
 build_equiv_class (bitset_t sbcset, const unsigned char *name)
 #endif /* not RE_ENABLE_I18N */
@@ -3798,7 +3804,7 @@ free_token (re_token_t *node)
    and its children. */

 static reg_errcode_t
-free_tree (void *extra, bin_tree_t *node)
+free_tree (void *extra _UNUSED_PARAMETER_, bin_tree_t *node)
 {
   free_token (&node->token);
   return REG_NOERROR;