diff --git a/tool/transport_common.cc b/tool/transport_common.cc
index ed1bc0f95..23fa3bb7a 100644
--- a/tool/transport_common.cc
+++ b/tool/transport_common.cc
@@ -535,8 +535,7 @@ bool DoSMTPStartTLS(int sock) {
   }
 
   // https://tools.ietf.org/html/rfc1869#section-4.3
-  if (reply_250.find("\nSTARTTLS\n") == std::string::npos &&
-      reply_250.find("\nSTARTTLS") != reply_250.size() - 8) {
+  if (("\n" + reply_250 + "\n").find("\nSTARTTLS\n") == std::string::npos) {
     fprintf(stderr, "Server does not support STARTTLS\n");
     return false;
   }