diff --git a/mercurial/parsers.c b/mercurial/parsers.c
--- a/mercurial/parsers.c
+++ b/mercurial/parsers.c
@@ -1166,7 +1166,9 @@ static PyObject *reachableroots(indexObj
 	/* Populate tovisit with all the heads */
 	numheads = PyList_GET_SIZE(heads);
 	for (i = 0; i < numheads; i++) {
-		revnum = PyInt_AS_LONG(PyList_GET_ITEM(heads, i));
+		revnum = PyInt_AsLong(PyList_GET_ITEM(heads, i));
+		if (revnum == -1 && PyErr_Occurred())
+			goto bail;
 		if (revnum + 1 < 0 || revnum + 1 >= len + 1) {
 			PyErr_SetString(PyExc_IndexError, "head out of range");
 			goto bail;
diff --git a/tests/test-parseindex.t b/tests/test-parseindex.t
--- a/tests/test-parseindex.t
+++ b/tests/test-parseindex.t
@@ -73,12 +73,12 @@ Test SEGV caused by bad revision passed 
   > for head in [0, len(cl) - 1, -1]:
   >     print'%s: %r' % (head, cl.reachableroots(0, [head], set([0])))
   > print 'bads:'
-  > for head in [len(cl), 10000, -2, -10000]:
+  > for head in [len(cl), 10000, -2, -10000, None]:
   >     print '%s:' % head,
   >     try:
   >         cl.reachableroots(0, [head], set([0]))
   >         print 'uncaught buffer overflow?'
-  >     except IndexError as inst:
+  >     except (IndexError, TypeError) as inst:
   >         print inst
   > EOF
   goods:
@@ -90,6 +90,7 @@ Test SEGV caused by bad revision passed 
   10000: head out of range
   -2: head out of range
   -10000: head out of range
+  None: an integer is required
 
   $ cd ..