diff --git a/test/agentmulti.py b/test/agentmulti.py
new file mode 100755
index 00000000..019bf2b6
--- /dev/null
+++ b/test/agentmulti.py
@@ -0,0 +1,56 @@
+#!/usr/bin/env python3
+
+import argparse
+import os
+import random
+import socket
+import sys
+
+from ssh import *
+
+def make_connections(n):
+    connections = []
+
+    for _ in range(n):
+        s = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        s.connect(os.environ["SSH_AUTH_SOCK"])
+        connections.append(s)
+
+    return connections
+
+def use_connection(s, idstring):
+    print("Trying {}...".format(idstring), end="")
+    sys.stdout.flush()
+
+    s.send(ssh_string(ssh_byte(SSH2_AGENTC_EXTENSION) + ssh_string(
+        b"nonexistent-agent-extension@putty.projects.tartarus.org")))
+    length = ssh_decode_uint32(s.recv(4))
+    assert length < AGENT_MAX_MSGLEN
+    msg = s.recv(length)
+    msgtype = msg[0]
+    msgstring = (
+        "SSH_AGENT_EXTENSION_FAILURE" if msgtype == SSH_AGENT_EXTENSION_FAILURE
+        else "SSH_AGENT_FAILURE" if msgtype == SSH_AGENT_FAILURE
+        else "type {:d}".format(msgtype))
+    print("got", msgstring, "with {:d}-byte payload".format(len(msg)-1))
+
+def randomly_use_connections(connections, iterations):
+    for _ in range(iterations):
+        index = random.randrange(0, len(connections))
+        s = connections[index]
+        use_connection(connections[index], "#{:d}".format(index))
+
+def main():
+    parser = argparse.ArgumentParser(
+        description='Test handling of multiple agent connections.')
+    parser.add_argument("--nsockets", type=int, default=128,
+                        help="Number of simultaneous connections to make.")
+    parser.add_argument("--ntries", type=int, default=1024,
+                        help="Number of messages to send in total.")
+    args = parser.parse_args()
+
+    connections = make_connections(args.nsockets)
+    randomly_use_connections(connections, args.ntries)
+
+if __name__ == '__main__':
+    main()
diff --git a/test/ssh.py b/test/ssh.py
index 90eccb7e..c4f2531f 100644
--- a/test/ssh.py
+++ b/test/ssh.py
@@ -88,6 +88,7 @@ SSH1_AGENTC_REMOVE_RSA_IDENTITY = 8
 SSH1_AGENTC_REMOVE_ALL_RSA_IDENTITIES = 9
 SSH_AGENT_FAILURE = 5
 SSH_AGENT_SUCCESS = 6
+SSH_AGENT_EXTENSION_FAILURE = 28
 SSH2_AGENTC_REQUEST_IDENTITIES = 11
 SSH2_AGENT_IDENTITIES_ANSWER = 12
 SSH2_AGENTC_SIGN_REQUEST = 13