diff --git a/sshagent/trezor.py b/sshagent/trezor.py
index 70b3891..80ad512 100644
--- a/sshagent/trezor.py
+++ b/sshagent/trezor.py
@@ -1,10 +1,6 @@
 import io
 import binascii
 
-from trezorlib.client import TrezorClient
-from trezorlib.transport_hid import HidTransport
-from trezorlib.types_pb2 import IdentityType
-
 from . import util
 from . import formats
 
@@ -12,14 +8,29 @@ import logging
 log = logging.getLogger(__name__)
 
 
-class Client(object):
+class TrezorLibrary(object):
 
-    def __init__(self):
+    @staticmethod
+    def client():
+        from trezorlib.client import TrezorClient
+        from trezorlib.transport_hid import HidTransport
         devices = HidTransport.enumerate()
         if len(devices) != 1:
             raise ValueError('{:d} Trezor devices found'.format(len(devices)))
-        client = TrezorClient(HidTransport(devices[0]))
-        f = client.features
+        return TrezorClient(HidTransport(devices[0]))
+
+    @staticmethod
+    def identity(label, proto='ssh'):
+        from trezorlib.types_pb2 import IdentityType
+        return IdentityType(host=label, proto=proto)
+
+
+class Client(object):
+
+    def __init__(self, factory=TrezorLibrary):
+        self.factory = factory
+        self.client = self.factory.client()
+        f = self.client.features
         log.info('connected to Trezor')
         log.debug('ID       : %s', f.device_id)
         log.debug('label    : %s', f.label)
@@ -27,19 +38,18 @@ class Client(object):
         version = [f.major_version, f.minor_version, f.patch_version]
         log.debug('version  : %s', '.'.join([str(v) for v in version]))
         log.debug('revision : %s', binascii.hexlify(f.revision))
-        self.client = client
 
     def close(self):
         self.client.close()
 
     def get_public_key(self, label):
-        addr = _get_address(_get_identity(label))
+        addr = _get_address(self.factory.identity(label))
         log.info('getting %r SSH public key from Trezor...', label)
         node = self.client.get_public_node(addr)
         return node.node.public_key
 
     def sign_ssh_challenge(self, label, blob):
-        ident = _get_identity(label)
+        ident = self.factory.identity(label)
         msg = _parse_ssh_blob(blob)
         request = 'user: "{user}"'.format(**msg)
 
@@ -54,10 +64,6 @@ class Client(object):
         return (r, s)
 
 
-def _get_identity(label, proto='ssh'):
-    return IdentityType(host=label, proto=proto)
-
-
 def _get_address(ident):
     index = '\x00' * 4
     addr = index + '{}://{}'.format(ident.proto, ident.host)
diff --git a/sshagent/trezor_agent.py b/sshagent/trezor_agent.py
index 2723248..46aa82f 100644
--- a/sshagent/trezor_agent.py
+++ b/sshagent/trezor_agent.py
@@ -22,7 +22,7 @@ def main():
     level = verbosity[min(args.verbose, len(verbosity) - 1)]
     logging.basicConfig(level=level, format=fmt)
 
-    client = trezor.Client()
+    client = trezor.Client(factory=trezor.TrezorLibrary)
 
     key_files = []
     for label in args.labels: