diff --git a/mercurial/parsers.c b/mercurial/parsers.c
--- a/mercurial/parsers.c
+++ b/mercurial/parsers.c
@@ -1713,6 +1713,15 @@ static int index_init(indexObject *self,
 	PyObject *data_obj, *inlined_obj;
 	Py_ssize_t size;
 
+	/* Initialize before argument-checking to avoid index_dealloc() crash. */
+	self->raw_length = 0;
+	self->added = NULL;
+	self->cache = NULL;
+	self->data = NULL;
+	self->headrevs = NULL;
+	self->nt = NULL;
+	self->offsets = NULL;
+
 	if (!PyArg_ParseTuple(args, "OO", &data_obj, &inlined_obj))
 		return -1;
 	if (!PyString_Check(data_obj)) {
@@ -1723,12 +1732,7 @@ static int index_init(indexObject *self,
 
 	self->inlined = inlined_obj && PyObject_IsTrue(inlined_obj);
 	self->data = data_obj;
-	self->cache = NULL;
 
-	self->added = NULL;
-	self->headrevs = NULL;
-	self->offsets = NULL;
-	self->nt = NULL;
 	self->ntlength = self->ntcapacity = 0;
 	self->ntdepth = self->ntsplits = 0;
 	self->ntlookups = self->ntmisses = 0;
@@ -1764,7 +1768,7 @@ static PyObject *index_nodemap(indexObje
 static void index_dealloc(indexObject *self)
 {
 	_index_clearcaches(self);
-	Py_DECREF(self->data);
+	Py_XDECREF(self->data);
 	Py_XDECREF(self->added);
 	PyObject_Del(self);
 }
diff --git a/tests/test-parseindex2.py b/tests/test-parseindex2.py
--- a/tests/test-parseindex2.py
+++ b/tests/test-parseindex2.py
@@ -98,6 +98,14 @@ def parse_index2(data, inline):
     return list(index), chunkcache
 
 def runtest() :
+    # Check that parse_index2() raises TypeError on bad arguments.
+    try:
+        parse_index2(0, True)
+    except TypeError:
+        pass
+    else:
+        print "Expected to get TypeError."
+
     py_res_1 = py_parseindex(data_inlined, True)
     c_res_1 = parse_index2(data_inlined, True)