diff --git a/src/wormhole/errors.py b/src/wormhole/errors.py
index 865b5e2..b6ba419 100644
--- a/src/wormhole/errors.py
+++ b/src/wormhole/errors.py
@@ -53,3 +53,9 @@ class NoTorError(WormholeError):
 
 class NoKeyError(WormholeError):
     """w.derive_key() was called before got_verifier() fired"""
+
+class WormholeClosed(Exception):
+    """Deferred-returning API calls errback with WormholeClosed if the
+    wormhole was already closed, or if it closes before a real result can be
+    obtained."""
+
diff --git a/src/wormhole/wormhole.py b/src/wormhole/wormhole.py
index d316daf..e73eb1b 100644
--- a/src/wormhole/wormhole.py
+++ b/src/wormhole/wormhole.py
@@ -10,7 +10,7 @@ from .timing import DebugTiming
 from .journal import ImmediateJournal
 from ._boss import Boss
 from ._key import derive_key
-from .errors import WelcomeError, NoKeyError
+from .errors import WelcomeError, NoKeyError, WormholeClosed
 from .util import to_bytes
 
 # We can provide different APIs to different apps:
@@ -131,9 +131,6 @@ class _DelegatedWormhole(object):
     def closed(self, result):
         self._delegate.wormhole_closed(result)
 
-class WormholeClosed(Exception):
-    pass
-
 @implementer(IWormhole)
 class _DeferredWormhole(object):
     def __init__(self):
@@ -146,6 +143,7 @@ class _DeferredWormhole(object):
         self._version_observers = []
         self._received_data = []
         self._received_observers = []
+        self._observer_result = None
         self._closed_result = None
         self._closed_observers = []
 
@@ -154,20 +152,28 @@ class _DeferredWormhole(object):
 
     # from above
     def when_code(self):
-        if self._code:
+        # TODO: consider throwing error unless one of allocate/set/input_code
+        # was called first
+        if self._observer_result is not None:
+            return defer.fail(self._observer_result)
+        if self._code is not None:
             return defer.succeed(self._code)
         d = defer.Deferred()
         self._code_observers.append(d)
         return d
 
     def when_verifier(self):
-        if self._verifier:
+        if self._observer_result is not None:
+            return defer.fail(self._observer_result)
+        if self._verifier is not None:
             return defer.succeed(self._verifier)
         d = defer.Deferred()
         self._verifier_observers.append(d)
         return d
 
     def when_version(self):
+        if self._observer_result is not None:
+            return defer.fail(self._observer_result)
         if self._version is not None:
             return defer.succeed(self._version)
         d = defer.Deferred()
@@ -175,6 +181,8 @@ class _DeferredWormhole(object):
         return d
 
     def when_received(self):
+        if self._observer_result is not None:
+            return defer.fail(self._observer_result)
         if self._received_data:
             return defer.succeed(self._received_data.pop(0))
         d = defer.Deferred()
@@ -209,9 +217,9 @@ class _DeferredWormhole(object):
         # WormholeError) if state=="scary".
         if self._closed_result:
             return defer.succeed(self._closed_result) # maybe Failure
-        self._boss.close() # only need to close if it wasn't already
         d = defer.Deferred()
         self._closed_observers.append(d)
+        self._boss.close() # only need to close if it wasn't already
         return d
 
     def debug_set_trace(self, client_name, which="B N M S O K R RC L C T",
@@ -248,18 +256,18 @@ class _DeferredWormhole(object):
     def closed(self, result):
         #print("closed", result, type(result))
         if isinstance(result, Exception):
-            observer_result = self._closed_result = failure.Failure(result)
+            self._observer_result = self._closed_result = failure.Failure(result)
         else:
             # pending w.verify()/w.version()/w.read() get an error
-            observer_result = WormholeClosed(result)
+            self._observer_result = WormholeClosed(result)
             # but w.close() only gets error if we're unhappy
             self._closed_result = result
         for d in self._verifier_observers:
-            d.errback(observer_result)
+            d.errback(self._observer_result)
         for d in self._version_observers:
-            d.errback(observer_result)
+            d.errback(self._observer_result)
         for d in self._received_observers:
-            d.errback(observer_result)
+            d.errback(self._observer_result)
         for d in self._closed_observers:
             d.callback(self._closed_result)