diff --git a/src/wormhole/errors.py b/src/wormhole/errors.py
index 08ebae7..2a271c6 100644
--- a/src/wormhole/errors.py
+++ b/src/wormhole/errors.py
@@ -36,6 +36,12 @@ class WrongPasswordError(Exception):
     # or the data blob was corrupted, and that's why decrypt failed
     pass
 
+class KeyFormatError(Exception):
+    """
+    The key you entered contains spaces. Magic-wormhole expects keys to be
+    separated by dashes.
+    """
+
 class ReflectionAttack(Exception):
     """An attacker (or bug) reflected our outgoing message back to us."""
 
diff --git a/src/wormhole/test/test_wormhole.py b/src/wormhole/test/test_wormhole.py
index ba54123..eae68af 100644
--- a/src/wormhole/test/test_wormhole.py
+++ b/src/wormhole/test/test_wormhole.py
@@ -7,7 +7,8 @@ from twisted.internet import reactor
 from twisted.internet.defer import Deferred, gatherResults, inlineCallbacks
 from .common import ServerBase
 from .. import wormhole
-from ..errors import WrongPasswordError, WelcomeError, UsageError
+from ..errors import (WrongPasswordError, WelcomeError, UsageError,
+                      KeyFormatError)
 from spake2 import SPAKE2_Symmetric
 from ..timing import DebugTiming
 from ..util import (bytes_to_dict, dict_to_bytes,
@@ -818,6 +819,20 @@ class Wormholes(ServerBase, unittest.TestCase):
         yield w2.close()
         self.flushLoggedErrors(WrongPasswordError)
 
+    @inlineCallbacks
+    def test_wrong_password_with_spaces(self):
+        w1 = wormhole.wormhole(APPID, self.relayurl, reactor)
+        w2 = wormhole.wormhole(APPID, self.relayurl, reactor)
+        code = yield w1.get_code()
+        code_no_dashes = code.replace('-', ' ')
+
+        with self.assertRaises(KeyFormatError):
+            w2.set_code(code_no_dashes)
+
+        yield w1.close()
+        yield w2.close()
+        self.flushLoggedErrors(ValueError)
+
     @inlineCallbacks
     def test_verifier(self):
         w1 = wormhole.wormhole(APPID, self.relayurl, reactor)
@@ -875,4 +890,3 @@ class Errors(ServerBase, unittest.TestCase):
         yield self.assertFailure(w.get_code(), UsageError)
         yield self.assertFailure(w.input_code(), UsageError)
         yield w.close()
-