diff --git a/mercurial/filelog.py b/mercurial/filelog.py
--- a/mercurial/filelog.py
+++ b/mercurial/filelog.py
@@ -7,16 +7,16 @@
 
 from __future__ import absolute_import
 
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     error,
     repository,
     revlog,
 )
+from .utils import (
+    interfaceutil,
+)
 
-@zi.implementer(repository.ifilestorage)
+@interfaceutil.implementer(repository.ifilestorage)
 class filelog(object):
     def __init__(self, opener, path):
         self._revlog = revlog.revlog(opener,
diff --git a/mercurial/httppeer.py b/mercurial/httppeer.py
--- a/mercurial/httppeer.py
+++ b/mercurial/httppeer.py
@@ -20,9 +20,6 @@ from .i18n import _
 from .thirdparty import (
     cbor,
 )
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     bundle2,
     error,
@@ -38,6 +35,9 @@ from . import (
     wireprotov2peer,
     wireprotov2server,
 )
+from .utils import (
+    interfaceutil,
+)
 
 httplib = util.httplib
 urlerr = util.urlerr
@@ -582,7 +582,7 @@ class queuedcommandfuture(pycompat.futur
         # will resolve to Future.result.
         return self.result(timeout)
 
-@zi.implementer(repository.ipeercommandexecutor)
+@interfaceutil.implementer(repository.ipeercommandexecutor)
 class httpv2executor(object):
     def __init__(self, ui, opener, requestbuilder, apiurl, descriptor):
         self._ui = ui
@@ -731,8 +731,9 @@ class httpv2executor(object):
             pass
 
 # TODO implement interface for version 2 peers
-@zi.implementer(repository.ipeerconnection, repository.ipeercapabilities,
-                repository.ipeerrequests)
+@interfaceutil.implementer(repository.ipeerconnection,
+                           repository.ipeercapabilities,
+                           repository.ipeerrequests)
 class httpv2peer(object):
     def __init__(self, ui, repourl, apipath, opener, requestbuilder,
                  apidescriptor):
diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
--- a/mercurial/localrepo.py
+++ b/mercurial/localrepo.py
@@ -21,9 +21,6 @@ from .node import (
     nullid,
     short,
 )
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     bookmarks,
     branchmap,
@@ -68,6 +65,7 @@ from . import (
     vfs as vfsmod,
 )
 from .utils import (
+    interfaceutil,
     procutil,
     stringutil,
 )
@@ -153,7 +151,7 @@ moderncaps = {'lookup', 'branchmap', 'pu
               'unbundle'}
 legacycaps = moderncaps.union({'changegroupsubset'})
 
-@zi.implementer(repository.ipeercommandexecutor)
+@interfaceutil.implementer(repository.ipeercommandexecutor)
 class localcommandexecutor(object):
     def __init__(self, peer):
         self._peer = peer
@@ -196,7 +194,7 @@ class localcommandexecutor(object):
     def close(self):
         self._closed = True
 
-@zi.implementer(repository.ipeercommands)
+@interfaceutil.implementer(repository.ipeercommands)
 class localpeer(repository.peer):
     '''peer for a local repo; reflects only the most recent API'''
 
@@ -324,7 +322,7 @@ class localpeer(repository.peer):
 
     # End of peer interface.
 
-@zi.implementer(repository.ipeerlegacycommands)
+@interfaceutil.implementer(repository.ipeerlegacycommands)
 class locallegacypeer(localpeer):
     '''peer extension which implements legacy methods too; used for tests with
     restricted capabilities'''
@@ -365,7 +363,7 @@ REVLOGV2_REQUIREMENT = 'exp-revlogv2.0'
 # set to reflect that the extension knows how to handle that requirements.
 featuresetupfuncs = set()
 
-@zi.implementer(repository.completelocalrepository)
+@interfaceutil.implementer(repository.completelocalrepository)
 class localrepository(object):
 
     # obsolete experimental requirements:
diff --git a/mercurial/repository.py b/mercurial/repository.py
--- a/mercurial/repository.py
+++ b/mercurial/repository.py
@@ -8,14 +8,14 @@
 from __future__ import absolute_import
 
 from .i18n import _
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     error,
 )
+from .utils import (
+    interfaceutil,
+)
 
-class ipeerconnection(zi.Interface):
+class ipeerconnection(interfaceutil.Interface):
     """Represents a "connection" to a repository.
 
     This is the base interface for representing a connection to a repository.
@@ -24,7 +24,7 @@ class ipeerconnection(zi.Interface):
     This is not a complete interface definition and should not be used
     outside of this module.
     """
-    ui = zi.Attribute("""ui.ui instance""")
+    ui = interfaceutil.Attribute("""ui.ui instance""")
 
     def url():
         """Returns a URL string representing this peer.
@@ -61,7 +61,7 @@ class ipeerconnection(zi.Interface):
         associated with the peer should be cleaned up.
         """
 
-class ipeercapabilities(zi.Interface):
+class ipeercapabilities(interfaceutil.Interface):
     """Peer sub-interface related to capabilities."""
 
     def capable(name):
@@ -81,7 +81,7 @@ class ipeercapabilities(zi.Interface):
         Raises a ``CapabilityError`` if the capability isn't present.
         """
 
-class ipeercommands(zi.Interface):
+class ipeercommands(interfaceutil.Interface):
     """Client-side interface for communicating over the wire protocol.
 
     This interface is used as a gateway to the Mercurial wire protocol.
@@ -170,7 +170,7 @@ class ipeercommands(zi.Interface):
         Returns the integer number of heads added to the peer.
         """
 
-class ipeerlegacycommands(zi.Interface):
+class ipeerlegacycommands(interfaceutil.Interface):
     """Interface for implementing support for legacy wire protocol commands.
 
     Wire protocol commands transition to legacy status when they are no longer
@@ -202,7 +202,7 @@ class ipeerlegacycommands(zi.Interface):
     def changegroupsubset(bases, heads, source):
         pass
 
-class ipeercommandexecutor(zi.Interface):
+class ipeercommandexecutor(interfaceutil.Interface):
     """Represents a mechanism to execute remote commands.
 
     This is the primary interface for requesting that wire protocol commands
@@ -259,7 +259,7 @@ class ipeercommandexecutor(zi.Interface)
         This method may call ``sendcommands()`` if there are buffered commands.
         """
 
-class ipeerrequests(zi.Interface):
+class ipeerrequests(interfaceutil.Interface):
     """Interface for executing commands on a peer."""
 
     def commandexecutor():
@@ -290,7 +290,7 @@ class ipeerbase(ipeerconnection, ipeerca
     All peer instances must conform to this interface.
     """
 
-@zi.implementer(ipeerbase)
+@interfaceutil.implementer(ipeerbase)
 class peer(object):
     """Base class for peer repositories."""
 
@@ -314,7 +314,7 @@ class peer(object):
             _('cannot %s; remote repository does not support the %r '
               'capability') % (purpose, name))
 
-class ifilerevisionssequence(zi.Interface):
+class ifilerevisionssequence(interfaceutil.Interface):
     """Contains index data for all revisions of a file.
 
     Types implementing this behave like lists of tuples. The index
@@ -365,7 +365,7 @@ class ifilerevisionssequence(zi.Interfac
     def insert(self, i, entry):
         """Add an item to the index at specific revision."""
 
-class ifileindex(zi.Interface):
+class ifileindex(interfaceutil.Interface):
     """Storage interface for index data of a single file.
 
     File storage data is divided into index metadata and data storage.
@@ -377,7 +377,7 @@ class ifileindex(zi.Interface):
     * DAG data (storing and querying the relationship between nodes).
     * Metadata to facilitate storage.
     """
-    index = zi.Attribute(
+    index = interfaceutil.Attribute(
         """An ``ifilerevisionssequence`` instance.""")
 
     def __len__():
@@ -470,7 +470,7 @@ class ifileindex(zi.Interface):
     def candelta(baserev, rev):
         """"Whether a delta can be generated between two revisions."""
 
-class ifiledata(zi.Interface):
+class ifiledata(interfaceutil.Interface):
     """Storage interface for data storage of a specific file.
 
     This complements ``ifileindex`` and provides an interface for accessing
@@ -536,7 +536,7 @@ class ifiledata(zi.Interface):
         revision data.
         """
 
-class ifilemutation(zi.Interface):
+class ifilemutation(interfaceutil.Interface):
     """Storage interface for mutation events of a tracked file."""
 
     def add(filedata, meta, transaction, linkrev, p1, p2):
@@ -608,13 +608,13 @@ class ifilemutation(zi.Interface):
 class ifilestorage(ifileindex, ifiledata, ifilemutation):
     """Complete storage interface for a single tracked file."""
 
-    version = zi.Attribute(
+    version = interfaceutil.Attribute(
         """Version number of storage.
 
         TODO this feels revlog centric and could likely be removed.
         """)
 
-    storedeltachains = zi.Attribute(
+    storedeltachains = interfaceutil.Attribute(
         """Whether the store stores deltas.
 
         TODO deltachains are revlog centric. This can probably removed
@@ -622,7 +622,7 @@ class ifilestorage(ifileindex, ifiledata
         data.
         """)
 
-    _generaldelta = zi.Attribute(
+    _generaldelta = interfaceutil.Attribute(
         """Whether deltas can be against any parent revision.
 
         TODO this is used by changegroup code and it could probably be
@@ -642,59 +642,59 @@ class ifilestorage(ifileindex, ifiledata
         TODO this is used by verify and it should not be part of the interface.
         """
 
-class completelocalrepository(zi.Interface):
+class completelocalrepository(interfaceutil.Interface):
     """Monolithic interface for local repositories.
 
     This currently captures the reality of things - not how things should be.
     """
 
-    supportedformats = zi.Attribute(
+    supportedformats = interfaceutil.Attribute(
         """Set of requirements that apply to stream clone.
 
         This is actually a class attribute and is shared among all instances.
         """)
 
-    openerreqs = zi.Attribute(
+    openerreqs = interfaceutil.Attribute(
         """Set of requirements that are passed to the opener.
 
         This is actually a class attribute and is shared among all instances.
         """)
 
-    supported = zi.Attribute(
+    supported = interfaceutil.Attribute(
         """Set of requirements that this repo is capable of opening.""")
 
-    requirements = zi.Attribute(
+    requirements = interfaceutil.Attribute(
         """Set of requirements this repo uses.""")
 
-    filtername = zi.Attribute(
+    filtername = interfaceutil.Attribute(
         """Name of the repoview that is active on this repo.""")
 
-    wvfs = zi.Attribute(
+    wvfs = interfaceutil.Attribute(
         """VFS used to access the working directory.""")
 
-    vfs = zi.Attribute(
+    vfs = interfaceutil.Attribute(
         """VFS rooted at the .hg directory.
 
         Used to access repository data not in the store.
         """)
 
-    svfs = zi.Attribute(
+    svfs = interfaceutil.Attribute(
         """VFS rooted at the store.
 
         Used to access repository data in the store. Typically .hg/store.
         But can point elsewhere if the store is shared.
         """)
 
-    root = zi.Attribute(
+    root = interfaceutil.Attribute(
         """Path to the root of the working directory.""")
 
-    path = zi.Attribute(
+    path = interfaceutil.Attribute(
         """Path to the .hg directory.""")
 
-    origroot = zi.Attribute(
+    origroot = interfaceutil.Attribute(
         """The filesystem path that was used to construct the repo.""")
 
-    auditor = zi.Attribute(
+    auditor = interfaceutil.Attribute(
         """A pathauditor for the working directory.
 
         This checks if a path refers to a nested repository.
@@ -702,40 +702,40 @@ class completelocalrepository(zi.Interfa
         Operates on the filesystem.
         """)
 
-    nofsauditor = zi.Attribute(
+    nofsauditor = interfaceutil.Attribute(
         """A pathauditor for the working directory.
 
         This is like ``auditor`` except it doesn't do filesystem checks.
         """)
 
-    baseui = zi.Attribute(
+    baseui = interfaceutil.Attribute(
         """Original ui instance passed into constructor.""")
 
-    ui = zi.Attribute(
+    ui = interfaceutil.Attribute(
         """Main ui instance for this instance.""")
 
-    sharedpath = zi.Attribute(
+    sharedpath = interfaceutil.Attribute(
         """Path to the .hg directory of the repo this repo was shared from.""")
 
-    store = zi.Attribute(
+    store = interfaceutil.Attribute(
         """A store instance.""")
 
-    spath = zi.Attribute(
+    spath = interfaceutil.Attribute(
         """Path to the store.""")
 
-    sjoin = zi.Attribute(
+    sjoin = interfaceutil.Attribute(
         """Alias to self.store.join.""")
 
-    cachevfs = zi.Attribute(
+    cachevfs = interfaceutil.Attribute(
         """A VFS used to access the cache directory.
 
         Typically .hg/cache.
         """)
 
-    filteredrevcache = zi.Attribute(
+    filteredrevcache = interfaceutil.Attribute(
         """Holds sets of revisions to be filtered.""")
 
-    names = zi.Attribute(
+    names = interfaceutil.Attribute(
         """A ``namespaces`` instance.""")
 
     def close():
@@ -750,19 +750,19 @@ class completelocalrepository(zi.Interfa
     def filtered(name, visibilityexceptions=None):
         """Obtain a named view of this repository."""
 
-    obsstore = zi.Attribute(
+    obsstore = interfaceutil.Attribute(
         """A store of obsolescence data.""")
 
-    changelog = zi.Attribute(
+    changelog = interfaceutil.Attribute(
         """A handle on the changelog revlog.""")
 
-    manifestlog = zi.Attribute(
+    manifestlog = interfaceutil.Attribute(
         """A handle on the root manifest revlog.""")
 
-    dirstate = zi.Attribute(
+    dirstate = interfaceutil.Attribute(
         """Working directory state.""")
 
-    narrowpats = zi.Attribute(
+    narrowpats = interfaceutil.Attribute(
         """Matcher patterns for this repository's narrowspec.""")
 
     def narrowmatch():
@@ -978,7 +978,7 @@ class completelocalrepository(zi.Interfa
     def checkpush(pushop):
         pass
 
-    prepushoutgoinghooks = zi.Attribute(
+    prepushoutgoinghooks = interfaceutil.Attribute(
         """util.hooks instance.""")
 
     def pushkey(namespace, key, old, new):
diff --git a/mercurial/utils/interfaceutil.py b/mercurial/utils/interfaceutil.py
new file mode 100644
--- /dev/null
+++ b/mercurial/utils/interfaceutil.py
@@ -0,0 +1,40 @@
+# interfaceutil.py - Utilities for declaring interfaces.
+#
+# Copyright 2018 Gregory Szorc <gregory.szorc@gmail.com>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+# zope.interface imposes a run-time cost due to module import overhead and
+# bookkeeping for declaring interfaces. So, we use stubs for various
+# zope.interface primitives unless instructed otherwise.
+
+from __future__ import absolute_import
+
+from .. import (
+    encoding,
+)
+
+if encoding.environ.get('HGREALINTERFACES'):
+    from ..thirdparty.zope import (
+        interface as zi,
+    )
+
+    Attribute = zi.Attribute
+    Interface = zi.Interface
+    implementer = zi.implementer
+else:
+    class Attribute(object):
+        def __init__(self, __name__, __doc__=''):
+            pass
+
+    class Interface(object):
+        def __init__(self, name, bases=(), attrs=None, __doc__=None,
+                 __module__=None):
+            pass
+
+    def implementer(*ifaces):
+        def wrapper(cls):
+            return cls
+
+        return wrapper
diff --git a/mercurial/wireprotoserver.py b/mercurial/wireprotoserver.py
--- a/mercurial/wireprotoserver.py
+++ b/mercurial/wireprotoserver.py
@@ -15,9 +15,6 @@ from .i18n import _
 from .thirdparty import (
     cbor,
 )
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     encoding,
     error,
@@ -29,6 +26,7 @@ from . import (
     wireprotov2server,
 )
 from .utils import (
+    interfaceutil,
     procutil,
 )
 
@@ -62,7 +60,7 @@ def decodevaluefromheaders(req, headerpr
 
     return ''.join(chunks)
 
-@zi.implementer(wireprototypes.baseprotocolhandler)
+@interfaceutil.implementer(wireprototypes.baseprotocolhandler)
 class httpv1protocolhandler(object):
     def __init__(self, req, ui, checkperm):
         self._req = req
@@ -489,7 +487,7 @@ def _sshv1respondooberror(fout, ferr, rs
     fout.write(b'\n')
     fout.flush()
 
-@zi.implementer(wireprototypes.baseprotocolhandler)
+@interfaceutil.implementer(wireprototypes.baseprotocolhandler)
 class sshv1protocolhandler(object):
     """Handler for requests services via version 1 of SSH protocol."""
     def __init__(self, ui, fin, fout):
diff --git a/mercurial/wireprototypes.py b/mercurial/wireprototypes.py
--- a/mercurial/wireprototypes.py
+++ b/mercurial/wireprototypes.py
@@ -9,14 +9,14 @@ from .node import (
     bin,
     hex,
 )
-from .thirdparty.zope import (
-    interface as zi,
-)
 from .i18n import _
 from . import (
     error,
     util,
 )
+from .utils import (
+    interfaceutil,
+)
 
 # Names of the SSH protocol implementations.
 SSHV1 = 'ssh-v1'
@@ -179,7 +179,7 @@ GETBUNDLE_ARGUMENTS = {
     'stream': 'boolean',
 }
 
-class baseprotocolhandler(zi.Interface):
+class baseprotocolhandler(interfaceutil.Interface):
     """Abstract base class for wire protocol handlers.
 
     A wire protocol handler serves as an interface between protocol command
@@ -188,7 +188,7 @@ class baseprotocolhandler(zi.Interface):
     the request, handle response types, etc.
     """
 
-    name = zi.Attribute(
+    name = interfaceutil.Attribute(
         """The name of the protocol implementation.
 
         Used for uniquely identifying the transport type.
diff --git a/mercurial/wireprotov1peer.py b/mercurial/wireprotov1peer.py
--- a/mercurial/wireprotov1peer.py
+++ b/mercurial/wireprotov1peer.py
@@ -15,9 +15,6 @@ from .i18n import _
 from .node import (
     bin,
 )
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     bundle2,
     changegroup as changegroupmod,
@@ -29,6 +26,9 @@ from . import (
     util,
     wireprototypes,
 )
+from .utils import (
+    interfaceutil,
+)
 
 urlreq = util.urlreq
 
@@ -110,7 +110,7 @@ class unsentfuture(pycompat.futures.Futu
         # on that.
         return self.result(timeout)
 
-@zi.implementer(repository.ipeercommandexecutor)
+@interfaceutil.implementer(repository.ipeercommandexecutor)
 class peerexecutor(object):
     def __init__(self, peer):
         self._peer = peer
@@ -308,7 +308,8 @@ class peerexecutor(object):
             else:
                 f.set_result(result)
 
-@zi.implementer(repository.ipeercommands, repository.ipeerlegacycommands)
+@interfaceutil.implementer(repository.ipeercommands,
+                           repository.ipeerlegacycommands)
 class wirepeer(repository.peer):
     """Client-side interface for communicating with a peer repository.
 
diff --git a/mercurial/wireprotov2server.py b/mercurial/wireprotov2server.py
--- a/mercurial/wireprotov2server.py
+++ b/mercurial/wireprotov2server.py
@@ -12,9 +12,6 @@ from .i18n import _
 from .thirdparty import (
     cbor,
 )
-from .thirdparty.zope import (
-    interface as zi,
-)
 from . import (
     encoding,
     error,
@@ -24,6 +21,9 @@ from . import (
     wireprotoframing,
     wireprototypes,
 )
+from .utils import (
+    interfaceutil,
+)
 
 FRAMINGTYPE = b'application/mercurial-exp-framing-0005'
 
@@ -340,7 +340,7 @@ def dispatch(repo, proto, command):
 
     return func(repo, proto, **args)
 
-@zi.implementer(wireprototypes.baseprotocolhandler)
+@interfaceutil.implementer(wireprototypes.baseprotocolhandler)
 class httpv2protocolhandler(object):
     def __init__(self, req, ui, args=None):
         self._req = req
diff --git a/tests/test-check-interfaces.py b/tests/test-check-interfaces.py
--- a/tests/test-check-interfaces.py
+++ b/tests/test-check-interfaces.py
@@ -2,6 +2,9 @@
 
 from __future__ import absolute_import, print_function
 
+from mercurial import encoding
+encoding.environ[b'HGREALINTERFACES'] = b'1'
+
 import os
 
 from mercurial.thirdparty.zope import (
diff --git a/tests/test-check-module-imports.t b/tests/test-check-module-imports.t
--- a/tests/test-check-module-imports.t
+++ b/tests/test-check-module-imports.t
@@ -27,6 +27,7 @@ outputs, which should be fixed later.
   > -X i18n/posplit \
   > -X mercurial/thirdparty \
   > -X tests/hypothesishelpers.py \
+  > -X tests/test-check-interfaces.py \
   > -X tests/test-commit-interactive.t \
   > -X tests/test-contrib-check-code.t \
   > -X tests/test-demandimport.py \