diff --git a/ext/standard/php_string.h b/ext/standard/php_string.h
index afb156ad7d8..51c537de6e6 100644
--- a/ext/standard/php_string.h
+++ b/ext/standard/php_string.h
@@ -42,7 +42,7 @@ PHPAPI zend_string *php_addcslashes(zend_string *str, const char *what, size_t w
 PHPAPI void php_stripcslashes(zend_string *str);
 PHPAPI zend_string *php_basename(const char *s, size_t len, const char *suffix, size_t sufflen);
 PHPAPI size_t php_dirname(char *str, size_t len);
-PHPAPI char *php_stristr(char *s, char *t, size_t s_len, size_t t_len);
+PHPAPI char *php_stristr(const char *s, const char *t, size_t s_len, size_t t_len);
 PHPAPI zend_string *php_str_to_str(const char *haystack, size_t length, const char *needle,
 		size_t needle_len, const char *str, size_t str_len);
 PHPAPI zend_string *php_trim(zend_string *str, const char *what, size_t what_len, int mode);
diff --git a/ext/standard/string.c b/ext/standard/string.c
index c84b0adec6a..9f7e0ff60d3 100644
--- a/ext/standard/string.c
+++ b/ext/standard/string.c
@@ -1669,7 +1669,7 @@ PHP_FUNCTION(pathinfo)
 
 /* {{{ php_stristr
    case insensitive strstr */
-PHPAPI char *php_stristr(char *s, char *t, size_t s_len, size_t t_len)
+PHPAPI char *php_stristr(const char *s, const char *t, size_t s_len, size_t t_len)
 {
 	return (char*)php_memnistr(s, t, t_len, s + s_len);
 }