diff --git a/asio/include/asio/ssl/impl/rfc2818_verification.ipp b/asio/include/asio/ssl/impl/rfc2818_verification.ipp
index 9b6ef04..e84cde6 100644
--- a/asio/include/asio/ssl/impl/rfc2818_verification.ipp
+++ b/asio/include/asio/ssl/impl/rfc2818_verification.ipp
@@ -54,7 +54,11 @@
   // or IP address entries.
   GENERAL_NAMES* gens = static_cast<GENERAL_NAMES*>(
       X509_get_ext_d2i(cert, NID_subject_alt_name, 0, 0));
+#if defined(OPENSSL_IS_BORINGSSL)
+  for (size_t i = 0; i < sk_GENERAL_NAME_num(gens); ++i)
+#else
   for (int i = 0; i < sk_GENERAL_NAME_num(gens); ++i)
+#endif
   {
     GENERAL_NAME* gen = sk_GENERAL_NAME_value(gens, i);
     if (gen->type == GEN_DNS && !is_address)