--- a/lib/regex_internal.c
+++ b/lib/regex_internal.c
@@ -36,7 +36,7 @@
    re_string_reconstruct before using the object.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_string_allocate (re_string_t *pstr, const char *str, Idx len, Idx init_len,
 		    RE_TRANSLATE_TYPE trans, bool icase, const re_dfa_t *dfa)
 {
@@ -64,7 +64,7 @@
 /* This function allocate the buffers, and initialize them.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_string_construct (re_string_t *pstr, const char *str, Idx len,
 		     RE_TRANSLATE_TYPE trans, bool icase, const re_dfa_t *dfa)
 {
@@ -127,7 +127,7 @@
 /* Helper functions for re_string_allocate, and re_string_construct.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_string_realloc_buffers (re_string_t *pstr, Idx new_buf_len)
 {
 #ifdef RE_ENABLE_I18N
@@ -267,7 +267,7 @@
    but for REG_ICASE.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 build_wcs_upper_buffer (re_string_t *pstr)
 {
   mbstate_t prev_st;
@@ -569,7 +569,7 @@
    convert to upper case in case of REG_ICASE, apply translation.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_string_reconstruct (re_string_t *pstr, Idx idx, int eflags)
 {
   Idx offset;
@@ -964,7 +964,7 @@
 /* Functions for set operation.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_alloc (re_node_set *set, Idx size)
 {
   set->alloc = size;
@@ -976,7 +976,7 @@
 }
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_init_1 (re_node_set *set, Idx elem)
 {
   set->alloc = 1;
@@ -992,7 +992,7 @@
 }
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_init_2 (re_node_set *set, Idx elem1, Idx elem2)
 {
   set->alloc = 2;
@@ -1022,7 +1022,7 @@
 }
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_init_copy (re_node_set *dest, const re_node_set *src)
 {
   dest->nelem = src->nelem;
@@ -1047,7 +1047,7 @@
    Note: We assume dest->elems is NULL, when dest->alloc is 0.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_add_intersect (re_node_set *dest, const re_node_set *src1,
 			   const re_node_set *src2)
 {
@@ -1138,7 +1138,7 @@
    DEST. Return value indicate the error code or REG_NOERROR if succeeded.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_init_union (re_node_set *dest, const re_node_set *src1,
 			const re_node_set *src2)
 {
@@ -1191,7 +1191,7 @@
    DEST. Return value indicate the error code or REG_NOERROR if succeeded.  */
 
 static reg_errcode_t
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_merge (re_node_set *dest, const re_node_set *src)
 {
   Idx is, id, sbase, delta;
@@ -1275,7 +1275,7 @@
    Return true if successful.  */
 
 static bool
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_insert (re_node_set *set, Idx elem)
 {
   Idx idx;
@@ -1327,7 +1327,7 @@
    Return true if successful.  */
 
 static bool
-internal_function
+internal_function __attribute_warn_unused_result__
 re_node_set_insert_last (re_node_set *set, Idx elem)
 {
   /* Realloc if we need.  */
@@ -1473,7 +1473,7 @@
 	   optimization.  */
 
 static re_dfastate_t *
-internal_function
+internal_function __attribute_warn_unused_result__
 re_acquire_state (reg_errcode_t *err, const re_dfa_t *dfa,
 		  const re_node_set *nodes)
 {
@@ -1521,7 +1521,7 @@
 	   optimization.  */
 
 static re_dfastate_t *
-internal_function
+internal_function __attribute_warn_unused_result__
 re_acquire_state_context (reg_errcode_t *err, const re_dfa_t *dfa,
 			  const re_node_set *nodes, unsigned int context)
 {
@@ -1562,6 +1562,7 @@
    indicates the error code if failed.  */
 
 static reg_errcode_t
+__attribute_warn_unused_result__
 register_state (const re_dfa_t *dfa, re_dfastate_t *newstate,
 		re_hashval_t hash)
 {
@@ -1616,7 +1617,7 @@
    Return the new state if succeeded, otherwise return NULL.  */
 
 static re_dfastate_t *
-internal_function
+internal_function __attribute_warn_unused_result__
 create_ci_newstate (const re_dfa_t *dfa, const re_node_set *nodes,
 		    re_hashval_t hash)
 {
@@ -1666,7 +1667,7 @@
    Return the new state if succeeded, otherwise return NULL.  */
 
 static re_dfastate_t *
-internal_function
+internal_function __attribute_warn_unused_result__
 create_cd_newstate (const re_dfa_t *dfa, const re_node_set *nodes,
 		    unsigned int context, re_hashval_t hash)
 {