diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -335,18 +335,17 @@ static PyObject *index_get(indexObject *
 	c_node_id = data + 32;
 
 	if (self->entry_size == v1_entry_size) {
-		return Py_BuildValue(v1_tuple_format, offset_flags, comp_len,
-		                     uncomp_len, base_rev, link_rev, parent_1,
-		                     parent_2, c_node_id, self->nodelen);
+		sidedata_offset = 0;
+		sidedata_comp_len = 0;
 	} else {
 		sidedata_offset = getbe64(data + 64);
 		sidedata_comp_len = getbe32(data + 72);
-
-		return Py_BuildValue(v2_tuple_format, offset_flags, comp_len,
-		                     uncomp_len, base_rev, link_rev, parent_1,
-		                     parent_2, c_node_id, self->nodelen,
-		                     sidedata_offset, sidedata_comp_len);
 	}
+
+	return Py_BuildValue(v2_tuple_format, offset_flags, comp_len,
+	                     uncomp_len, base_rev, link_rev, parent_1, parent_2,
+	                     c_node_id, self->nodelen, sidedata_offset,
+	                     sidedata_comp_len);
 }
 /*
  * Pack header information in binary
@@ -2769,15 +2768,9 @@ static int index_init(indexObject *self,
 		self->entry_size = v1_entry_size;
 	}
 
-	if (self->format_version == format_v1) {
-		self->nullentry =
-		    Py_BuildValue(PY23("iiiiiiis#", "iiiiiiiy#"), 0, 0, 0, -1,
-		                  -1, -1, -1, nullid, self->nodelen);
-	} else {
-		self->nullentry =
-		    Py_BuildValue(PY23("iiiiiiis#ii", "iiiiiiiy#ii"), 0, 0, 0,
-		                  -1, -1, -1, -1, nullid, self->nodelen, 0, 0);
-	}
+	self->nullentry =
+	    Py_BuildValue(PY23("iiiiiiis#ii", "iiiiiiiy#ii"), 0, 0, 0, -1, -1,
+	                  -1, -1, nullid, self->nodelen, 0, 0);
 
 	if (!self->nullentry)
 		return -1;
diff --git a/mercurial/pure/parsers.py b/mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py
+++ b/mercurial/pure/parsers.py
@@ -53,7 +53,7 @@ class BaseIndexObject(object):
     # Size of a C long int, platform independent
     int_size = struct.calcsize(b'>i')
     # An empty index entry, used as a default value to be overridden, or nullrev
-    null_item = (0, 0, 0, -1, -1, -1, -1, sha1nodeconstants.nullid)
+    null_item = (0, 0, 0, -1, -1, -1, -1, sha1nodeconstants.nullid, 0, 0)
 
     @util.propertycache
     def entry_size(self):
@@ -122,11 +122,16 @@ class BaseIndexObject(object):
         else:
             index = self._calculate_index(i)
             data = self._data[index : index + self.entry_size]
-        r = self.index_format.unpack(data)
+        r = self._unpack_entry(data)
         if self._lgt and i == 0:
             r = (offset_type(0, gettype(r[0])),) + r[1:]
         return r
 
+    def _unpack_entry(self, data):
+        r = self.index_format.unpack(data)
+        r = r + (0, 0)
+        return r
+
     def pack_header(self, header):
         """pack header information as binary"""
         v_fmt = revlog_constants.INDEX_HEADER
@@ -135,7 +140,7 @@ class BaseIndexObject(object):
     def entry_binary(self, rev):
         """return the raw binary string representing a revision"""
         entry = self[rev]
-        p = revlog_constants.INDEX_ENTRY_V1.pack(*entry)
+        p = revlog_constants.INDEX_ENTRY_V1.pack(*entry[:8])
         if rev == 0:
             p = p[revlog_constants.INDEX_HEADER.size :]
         return p
@@ -266,7 +271,6 @@ def parse_index2(data, inline, revlogv2=
 
 class Index2Mixin(object):
     index_format = revlog_constants.INDEX_ENTRY_V2
-    null_item = (0, 0, 0, -1, -1, -1, -1, sha1nodeconstants.nullid, 0, 0)
 
     def replace_sidedata_info(
         self, i, sidedata_offset, sidedata_length, offset_flags
@@ -292,6 +296,9 @@ class Index2Mixin(object):
             msg = b"cannot rewrite entries outside of this transaction"
             raise KeyError(msg)
 
+    def _unpack_entry(self, data):
+        return self.index_format.unpack(data)
+
     def entry_binary(self, rev):
         """return the raw binary string representing a revision"""
         entry = self[rev]
diff --git a/mercurial/revlogutils/revlogv0.py b/mercurial/revlogutils/revlogv0.py
--- a/mercurial/revlogutils/revlogv0.py
+++ b/mercurial/revlogutils/revlogv0.py
@@ -135,6 +135,8 @@ def parse_index_v0(data, inline):
             nodemap.get(e[4], node.nullrev),
             nodemap.get(e[5], node.nullrev),
             e[6],
+            0,  # no side data support
+            0,  # no side data support
         )
         index.append(e2)
         nodemap[e[6]] = n
diff --git a/mercurial/unionrepo.py b/mercurial/unionrepo.py
--- a/mercurial/unionrepo.py
+++ b/mercurial/unionrepo.py
@@ -54,7 +54,18 @@ class unionrevlog(revlog.revlog):
         for rev2 in self.revlog2:
             rev = self.revlog2.index[rev2]
             # rev numbers - in revlog2, very different from self.rev
-            _start, _csize, rsize, base, linkrev, p1rev, p2rev, node = rev
+            (
+                _start,
+                _csize,
+                rsize,
+                base,
+                linkrev,
+                p1rev,
+                p2rev,
+                node,
+                _sdo,
+                _sds,
+            ) = rev
             flags = _start & 0xFFFF
 
             if linkmapper is None:  # link is to same revlog
diff --git a/tests/test-parseindex2.py b/tests/test-parseindex2.py
--- a/tests/test-parseindex2.py
+++ b/tests/test-parseindex2.py
@@ -49,6 +49,7 @@ def py_parseindex(data, inline):
         cache = (0, data)
         while off <= l:
             e = struct.unpack(indexformatng, data[off : off + s])
+            e = e + (0, 0)
             nodemap[e[7]] = n
             append(e)
             n += 1
@@ -58,6 +59,7 @@ def py_parseindex(data, inline):
     else:
         while off <= l:
             e = struct.unpack(indexformatng, data[off : off + s])
+            e = e + (0, 0)
             nodemap[e[7]] = n
             append(e)
             n += 1
@@ -240,7 +242,7 @@ class parseindex2tests(unittest.TestCase
                 break
 
     def testminusone(self):
-        want = (0, 0, 0, -1, -1, -1, -1, sha1nodeconstants.nullid)
+        want = (0, 0, 0, -1, -1, -1, -1, sha1nodeconstants.nullid, 0, 0)
         index, junk = parsers.parse_index2(data_inlined, True)
         got = index[-1]
         self.assertEqual(want, got)  # inline data