diff --git a/mercurial/cext/revlog.c b/mercurial/cext/revlog.c
--- a/mercurial/cext/revlog.c
+++ b/mercurial/cext/revlog.c
@@ -2073,6 +2073,21 @@
 	return PyBool_FromLong((long)ret);
 }
 
+static PyObject *index_m_rev(indexObject *self, PyObject *val)
+{
+	char *node;
+	int rev;
+
+	if (node_check(val, &node) == -1)
+		return NULL;
+	rev = index_find_node(self, node, 20);
+	if (rev >= -1)
+		return PyInt_FromLong(rev);
+	if (rev == -2)
+		raise_revlog_error();
+	return NULL;
+}
+
 typedef uint64_t bitmask;
 
 /*
@@ -2733,6 +2748,8 @@
     {"get", (PyCFunction)index_m_get, METH_VARARGS, "get an index entry"},
     {"has_node", (PyCFunction)index_m_has_node, METH_O,
      "return True if the node exist in the index"},
+    {"rev", (PyCFunction)index_m_rev, METH_O,
+     "return `rev` associated with a node or raise RevlogError"},
     {"computephasesmapsets", (PyCFunction)compute_phases_map_sets, METH_VARARGS,
      "compute phases"},
     {"reachableroots2", (PyCFunction)reachableroots2, METH_VARARGS,
diff --git a/mercurial/pure/parsers.py b/mercurial/pure/parsers.py
--- a/mercurial/pure/parsers.py
+++ b/mercurial/pure/parsers.py
@@ -59,6 +59,12 @@
         """return True if the node exist in the index"""
         return node in self.nodemap
 
+    def rev(self, node):
+        """return a revision for a node
+
+        If the node is unknown, raise a RevlogError"""
+        return self.nodemap[node]
+
     def _stripnodes(self, start):
         if 'nodemap' in vars(self):
             for r in range(start, len(self)):
diff --git a/mercurial/revlog.py b/mercurial/revlog.py
--- a/mercurial/revlog.py
+++ b/mercurial/revlog.py
@@ -217,6 +217,12 @@
         """return True if the node exist in the index"""
         return node in self.nodemap
 
+    def rev(self, node):
+        """return a revision for a node
+
+        If the node is unknown, raise a RevlogError"""
+        return self.nodemap[node]
+
     def append(self, tup):
         self.nodemap[tup[7]] = len(self)
         super(revlogoldindex, self).append(tup)