diff --git a/tool/server.cc b/tool/server.cc
index b6ed284a..0061cb34 100644
--- a/tool/server.cc
+++ b/tool/server.cc
@@ -79,6 +79,10 @@ static const struct argument kArguments[] = {
         "-debug", kBooleanArgument,
         "Print debug information about the handshake",
     },
+    {
+        "-require-any-client-cert", kBooleanArgument,
+        "The server will require a client certificate.",
+    },
     {
         "", kOptionalArgument, "",
     },
@@ -320,6 +324,14 @@ bool Server(const std::vector<std::string> &args) {
     SSL_CTX_set_info_callback(ctx.get(), InfoCallback);
   }
 
+  if (args_map.count("-require-any-client-cert") != 0) {
+    SSL_CTX_set_verify(
+        ctx.get(), SSL_VERIFY_PEER | SSL_VERIFY_FAIL_IF_NO_PEER_CERT, nullptr);
+    SSL_CTX_set_cert_verify_callback(
+        ctx.get(), [](X509_STORE_CTX *store, void *arg) -> int { return 1; },
+        nullptr);
+  }
+
   Listener listener;
   if (!listener.Init(args_map["-accept"])) {
     return false;