--- a/hghooks/mozhghooks/check/prevent_cross_channel_messages.py
+++ b/hghooks/mozhghooks/check/prevent_cross_channel_messages.py
@@ -30,17 +30,17 @@ class XChannelMessageCheck(PreTxnChangeg
     def name(self):
         return 'x_channel_message'
 
     def relevant(self):
         return (
             self.repo_metadata['firefox']
             or self.repo_metadata['thunderbird'])
 
-    def pre(self):
+    def pre(self, node):
         pass
 
     def check(self, ctx):
         if not any(line.startswith('X-Channel-')
                    for line in ctx.description().splitlines()):
             return True
 
         print_banner(self.ui, 'error', X_CHANNEL_COMMIT_FOUND)

--- a/hghooks/mozhghooks/check/prevent_ftl_changes.py
+++ b/hghooks/mozhghooks/check/prevent_ftl_changes.py
@@ -44,17 +44,17 @@ class FTLCheck(PreTxnChangegroupCheck):
     """
     @property
     def name(self):
         return 'ftl_check'
 
     def relevant(self):
         return self.repo_metadata['firefox_releasing']
 
-    def pre(self):
+    def pre(self, node):
         pass
 
     def check(self, ctx):
         if len(ctx.parents()) > 1:
             # Skip merge changesets
             return True
 
         if is_backout(ctx.description()):

--- a/hghooks/mozhghooks/check/prevent_subrepos.py
+++ b/hghooks/mozhghooks/check/prevent_subrepos.py
@@ -33,17 +33,17 @@ class PreventSubReposCheck(PreTxnChangeg
     """
     @property
     def name(self):
         return 'prevent_subrepos'
 
     def relevant(self):
         return True
 
-    def pre(self):
+    def pre(self, node):
         self.done = False
 
     def check(self, ctx):
         # Since the check can be non-fatal and since it requires a manifest
         # (which can be expensive to obtain), no-op if there is no work to do.
         if self.done:
             return True
 

--- a/hghooks/mozhghooks/check/prevent_symlinks.py
+++ b/hghooks/mozhghooks/check/prevent_symlinks.py
@@ -32,17 +32,17 @@ class PreventSymlinksCheck(PreTxnChangeg
 
     @property
     def name(self):
         return 'prevent_symlinks'
 
     def relevant(self):
         return not self.repo_metadata['user_repo']
 
-    def pre(self):
+    def pre(self, node):
         pass
 
     def check(self, ctx):
         manifest = ctx.manifest()
         links = []
 
         for f in ctx.files():
             if f not in manifest:

--- a/hghooks/mozhghooks/check/prevent_wptsync_changes.py
+++ b/hghooks/mozhghooks/check/prevent_wptsync_changes.py
@@ -40,17 +40,17 @@ class WPTSyncCheck(PreTxnChangegroupChec
     """
     @property
     def name(self):
         return 'wptsync_check'
 
     def relevant(self):
         return os.environ['USER'] == 'wptsync@mozilla.com'
 
-    def pre(self):
+    def pre(self, node):
         pass
 
     def check(self, ctx):
         success = False
         if self.repo_metadata['path'] == 'try':
             success = True
         elif self.repo_metadata['path'] == 'integration/mozilla-inbound':
             invalid_paths = [path for path in ctx.files() if not allowed_paths.match(path)]

--- a/hghooks/mozhghooks/check/single_root.py
+++ b/hghooks/mozhghooks/check/single_root.py
@@ -38,17 +38,17 @@ class SingleRootCheck(PreTxnChangegroupC
     """
     @property
     def name(self):
         return 'single_root'
 
     def relevant(self):
         return not self.repo_metadata['user_repo']
 
-    def pre(self):
+    def pre(self, node):
         self.new_roots = set()
 
     def check(self, ctx):
         if ctx.rev() != 0 and ctx.p1().node() == nullid:
             self.new_roots.add(ctx.node())
 
         return True
 

--- a/hghooks/mozhghooks/check/try_task_config_file.py
+++ b/hghooks/mozhghooks/check/try_task_config_file.py
@@ -26,17 +26,17 @@ class TryConfigCheck(PreTxnChangegroupCh
     """
     @property
     def name(self):
         return 'try_task_config'
 
     def relevant(self):
         return self.repo_metadata['firefox_releasing']
 
-    def pre(self):
+    def pre(self, node):
         pass
 
     def check(self, ctx):
         if 'try_task_config.json' not in ctx.files():
             return True
 
         print_banner(self.ui, 'error', TRY_CONFIG_FOUND)
         return False

--- a/hghooks/mozhghooks/checks.py
+++ b/hghooks/mozhghooks/checks.py
@@ -57,29 +57,34 @@ class PreTxnChangegroupCheck(object):
 
         Returns True if the check should run. False otherwise.
 
         The return value of this method is tightly validated to help prevent
         logic bugs.
         """
 
     @abc.abstractmethod
-    def pre(self):
+    def pre(self, node):
         """Called once before any changesets are examined.
 
         Allows derived classes to set additional instance state without having
         to call parent methods.
 
+        `node` - the first changeset in the group that was added (as per
+                 pretxnchangegroup).
+
         Return value is ignored.
         """
 
     @abc.abstractmethod
     def check(self, ctx):
         """Verifies a single changeset.
 
+        `ctx` - changectx object.
+
         Returns True if the check passes. False otherwise.
         """
 
     @abc.abstractmethod
     def post_check(self):
         """Called after all changesets have been checked.
 
         If the check gathers state during per-changeset invocations and needs

--- a/hghooks/mozhghooks/extension.py
+++ b/hghooks/mozhghooks/extension.py
@@ -124,17 +124,17 @@ def get_checks(ui, repo, source, classes
     return checks
 
 
 def pretxnchangegroup(ui, repo, node, source=None, **kwargs):
     checks = get_checks(ui, repo, source,
                         get_check_classes('pretxnchangegroup'))
 
     for check in checks:
-        check.pre()
+        check.pre(node)
 
     for rev in repo.changelog.revs(repo[node].rev()):
         ctx = repo[rev]
 
         for check in checks:
             if not check.check(ctx):
                 return 1