diff --git a/hgext/narrow/narrowcommands.py b/hgext/narrow/narrowcommands.py
--- a/hgext/narrow/narrowcommands.py
+++ b/hgext/narrow/narrowcommands.py
@@ -293,7 +293,7 @@
         else:
             known = []
             if ellipsesremote:
-                known = [node.hex(ctx.node()) for ctx in
+                known = [ctx.node() for ctx in
                          repo.set('::%ln', common)
                          if ctx.node() != node.nullid]
             with remote.commandexecutor() as e:
diff --git a/hgext/narrow/narrowwirepeer.py b/hgext/narrow/narrowwirepeer.py
--- a/hgext/narrow/narrowwirepeer.py
+++ b/hgext/narrow/narrowwirepeer.py
@@ -13,7 +13,6 @@
     extensions,
     hg,
     narrowspec,
-    node as nodemod,
     pycompat,
     wireprototypes,
     wireprotov1peer,
@@ -61,10 +60,13 @@
 
     preferuncompressed = False
     try:
-        oldincludes = wireprototypes.decodelist(oldincludes)
-        newincludes = wireprototypes.decodelist(newincludes)
-        oldexcludes = wireprototypes.decodelist(oldexcludes)
-        newexcludes = wireprototypes.decodelist(newexcludes)
+        def splitpaths(data):
+            # work around ''.split(',') => ['']
+            return data.split(b',') if data else []
+        oldincludes = splitpaths(oldincludes)
+        newincludes = splitpaths(newincludes)
+        oldexcludes = splitpaths(oldexcludes)
+        newexcludes = splitpaths(newexcludes)
         # validate the patterns
         narrowspec.validatepatterns(set(oldincludes))
         narrowspec.validatepatterns(set(newincludes))
@@ -73,7 +75,6 @@
 
         common = wireprototypes.decodelist(commonheads)
         known = wireprototypes.decodelist(known)
-        known = {nodemod.bin(n) for n in known}
         if ellipses == '0':
             ellipses = False
         else:
@@ -106,10 +107,12 @@
                                     prefer_uncompressed=preferuncompressed)
 
 def peernarrowwiden(remote, **kwargs):
-    for ch in (r'oldincludes', r'newincludes', r'oldexcludes', r'newexcludes',
-               r'commonheads', r'known'):
+    for ch in (r'commonheads', r'known'):
         kwargs[ch] = wireprototypes.encodelist(kwargs[ch])
 
+    for ch in (r'oldincludes', r'newincludes', r'oldexcludes', r'newexcludes'):
+        kwargs[ch] = b','.join(kwargs[ch])
+
     kwargs[r'ellipses'] = '%i' % bool(kwargs[r'ellipses'])
     f = remote._callcompressable('narrow_widen', **kwargs)
     return bundle2.getunbundler(remote.ui, f)
diff --git a/relnotes/next b/relnotes/next
--- a/relnotes/next
+++ b/relnotes/next
@@ -15,5 +15,9 @@
    you can override it by setting `$HGTEST_SHELL` or by passing it to
    `run-tests.py --shell <shell>`.
 
+ * The (experimental) narrow extension's wire protocol changed. If
+   you're using it, you'll need to make sure to upgrade server and
+   client at the same time.
+
 == Internal API Changes ==