diff --git a/talk/base/openssladapter.cc b/talk/base/openssladapter.cc
index 7e27fe3b19..7623d1a7a7 100644
--- a/talk/base/openssladapter.cc
+++ b/talk/base/openssladapter.cc
@@ -712,7 +712,10 @@ bool OpenSSLAdapter::VerifyServerName(SSL* ssl, const char* host,
       }
 
       STACK_OF(CONF_VALUE)* value = meth->i2v(meth, ext_str, NULL);
-      for (int j = 0; j < sk_CONF_VALUE_num(value); ++j) {
+
+      // Cast to size_t to be compilable for both OpenSSL and BoringSSL.
+      for (size_t j = 0; j < static_cast<size_t>(sk_CONF_VALUE_num(value));
+           ++j) {
         CONF_VALUE* nval = sk_CONF_VALUE_value(value, j);
         // The value for nval can contain wildcards
         if (!strcmp(nval->name, "DNS") && string_match(host, nval->value)) {