diff --git a/tool/client.cc b/tool/client.cc
index f4d1441..a95e04e 100644
--- a/tool/client.cc
+++ b/tool/client.cc
@@ -117,10 +117,16 @@
     },
     {
         "-root-certs", kOptionalArgument,
-        "A filename containing one of more PEM root certificates. Implies that "
+        "A filename containing one or more PEM root certificates. Implies that "
         "verification is required.",
     },
     {
+        "-root-cert-dir", kOptionalArgument,
+        "A directory containing one or more root certificate PEM files in "
+        "OpenSSL's hashed-directory format. Implies that verification is "
+        "required.",
+    },
+    {
         "-early-data", kOptionalArgument, "Enable early data. The argument to "
         "this flag is the early data to send or if it starts with '@', the "
         "file to read from for early data.",
@@ -500,6 +506,16 @@
     SSL_CTX_set_verify(ctx.get(), SSL_VERIFY_PEER, nullptr);
   }
 
+  if (args_map.count("-root-cert-dir") != 0) {
+    if (!SSL_CTX_load_verify_locations(
+            ctx.get(), nullptr, args_map["-root-cert-dir"].c_str())) {
+      fprintf(stderr, "Failed to load root certificates.\n");
+      ERR_print_errors_fp(stderr);
+      return false;
+    }
+    SSL_CTX_set_verify(ctx.get(), SSL_VERIFY_PEER, nullptr);
+  }
+
   if (args_map.count("-early-data") != 0) {
     SSL_CTX_set_early_data_enabled(ctx.get(), 1);
   }