diff --git a/trezor_agent/gpg/keyring.py b/trezor_agent/gpg/keyring.py
index 90e9848..f5053dc 100644
--- a/trezor_agent/gpg/keyring.py
+++ b/trezor_agent/gpg/keyring.py
@@ -34,6 +34,8 @@ def _recvline(sock):
 
     while True:
         c = sock.recv(1)
+        if not c:
+            raise EOFError
         if c == b'\n':
             break
         reply.write(c)
@@ -105,7 +107,7 @@ def parse_sig(sig):
     return parser(args=sig[1:])
 
 
-def sign_digest(sock, keygrip, digest, sp=subprocess):
+def sign_digest(sock, keygrip, digest, sp=subprocess, environ=None):
     """Sign a digest using specified key using GPG agent."""
     hash_algo = 8  # SHA256
     assert len(digest) == 32
@@ -115,7 +117,7 @@ def sign_digest(sock, keygrip, digest, sp=subprocess):
     ttyname = sp.check_output(['tty']).strip()
     options = ['ttyname={}'.format(ttyname)]  # set TTY for passphrase entry
 
-    display = os.environ.get('DISPLAY')
+    display = (environ or os.environ).get('DISPLAY')
     if display is not None:
         options.append('display={}'.format(display))
 
@@ -127,9 +129,8 @@ def sign_digest(sock, keygrip, digest, sp=subprocess):
     assert _communicate(sock, 'SETHASH {} {}'.format(hash_algo,
                                                      hex_digest)) == b'OK'
 
-    desc = ('Please+enter+the+passphrase+to+unlock+the+OpenPGP%0A'
-            'secret+key,+to+sign+a+new+TREZOR-based+subkey')
-    assert _communicate(sock, 'SETKEYDESC {}'.format(desc)) == b'OK'
+    assert _communicate(sock, 'SETKEYDESC '
+                        'Sign+a+new+TREZOR-based+subkey') == b'OK'
     assert _communicate(sock, 'PKSIGN') == b'OK'
     line = _recvline(sock).strip()
     line = unescape(line)
diff --git a/trezor_agent/gpg/tests/test_keyring.py b/trezor_agent/gpg/tests/test_keyring.py
index b312a5b..53a7c86 100644
--- a/trezor_agent/gpg/tests/test_keyring.py
+++ b/trezor_agent/gpg/tests/test_keyring.py
@@ -1,3 +1,6 @@
+import io
+import mock
+
 from .. import keyring
 
 
@@ -35,3 +38,39 @@ def test_parse_rsa():
     assert sig == [b'sig-val', [b'rsa', [b's', b'\x01\x02\x03\x04']]]
     assert rest == b''
     assert keyring.parse_sig(sig) == (0x1020304,)
+
+
+class FakeSocket(object):
+    def __init__(self):
+        self.rx = io.BytesIO()
+        self.tx = io.BytesIO()
+
+    def recv(self, n):
+        return self.rx.read(n)
+
+    def sendall(self, data):
+        self.tx.write(data)
+
+
+def test_sign_digest():
+    sock = FakeSocket()
+    sock.rx.write(b'OK Pleased to meet you, process XYZ\n')
+    sock.rx.write(b'OK\n' * 6)
+    sock.rx.write(b'D (7:sig-val(3:rsa(1:s16:0123456789ABCDEF)))\n')
+    sock.rx.seek(0)
+    keygrip = '1234'
+    digest = b'A' * 32
+    sp = mock.Mock(spec=['check_output'])
+    sp.check_output.return_value = '/dev/pts/0'
+    sig = keyring.sign_digest(sock=sock, keygrip=keygrip,
+                              digest=digest, sp=sp,
+                              environ={'DISPLAY': ':0'})
+    assert sig == (0x30313233343536373839414243444546,)
+    assert sock.tx.getvalue() == b'''RESET
+OPTION ttyname=/dev/pts/0
+OPTION display=:0
+SIGKEY 1234
+SETHASH 8 4141414141414141414141414141414141414141414141414141414141414141
+SETKEYDESC Sign+a+new+TREZOR-based+subkey
+PKSIGN
+'''