diff --git a/sapi/phpdbg/phpdbg_prompt.c b/sapi/phpdbg/phpdbg_prompt.c
index d7d0542cdf5..b242e5345a1 100644
--- a/sapi/phpdbg/phpdbg_prompt.c
+++ b/sapi/phpdbg/phpdbg_prompt.c
@@ -1417,7 +1417,7 @@ PHPDBG_COMMAND(register) /* {{{ */
 {
 	zend_function *function;
 	char *lcname = zend_str_tolower_dup(param->str, param->len);
-	size_t lcname_len = strlen(lcname);
+	size_t lcname_len = param->len;
 
 	if (!zend_hash_str_exists(&PHPDBG_G(registered), lcname, lcname_len)) {
 		if ((function = zend_hash_str_find_ptr(EG(function_table), lcname, lcname_len))) {