diff --git a/src/wormhole/cli/runner.py b/src/wormhole/cli/runner.py
index ac984c1..a15a50e 100644
--- a/src/wormhole/cli/runner.py
+++ b/src/wormhole/cli/runner.py
@@ -4,7 +4,8 @@ start = time.time()
 import os, sys, textwrap
 from twisted.internet.defer import maybeDeferred
 from twisted.internet.task import react
-from ..errors import TransferError, WrongPasswordError, WelcomeError, Timeout
+from ..errors import (TransferError, WrongPasswordError, WelcomeError, Timeout,
+                      KeyFormatError)
 from ..timing import DebugTiming
 from .cli_args import parser
 top_import_finish = time.time()
@@ -49,7 +50,8 @@ def run(reactor, argv, cwd, stdout, stderr, executable=None):
     d.addBoth(_maybe_dump_timing)
     def _explain_error(f):
         # these errors don't print a traceback, just an explanation
-        f.trap(TransferError, WrongPasswordError, WelcomeError, Timeout)
+        f.trap(TransferError, WrongPasswordError, WelcomeError, Timeout,
+               KeyFormatError)
         if f.check(WrongPasswordError):
             msg = textwrap.fill("ERROR: " + textwrap.dedent(f.value.__doc__))
             print(msg, file=stderr)
diff --git a/src/wormhole/wormhole.py b/src/wormhole/wormhole.py
index fafb966..1607413 100644
--- a/src/wormhole/wormhole.py
+++ b/src/wormhole/wormhole.py
@@ -15,7 +15,7 @@ from . import __version__
 from . import codes
 #from .errors import ServerError, Timeout
 from .errors import (WrongPasswordError, UsageError, WelcomeError,
-                     WormholeClosedError)
+                     WormholeClosedError, KeyFormatError)
 from .timing import DebugTiming
 from .util import (to_bytes, bytes_to_hexstr, hexstr_to_bytes,
                    dict_to_bytes, bytes_to_dict)
@@ -476,6 +476,13 @@ class _Wormhole:
 
     def _event_learned_code(self, code):
         self._timing.add("code established")
+        # bail out early if the password contains spaces...
+        # this should raise a useful error
+        if ' ' in code:
+            raise KeyFormatError(
+                "code (%s) contains spaces. Words must be separated by dashes"
+                % code
+            )
         self._code = code
         mo = re.search(r'^(\d+)-', code)
         if not mo: