--- vmd-1.8.6/src/py_atomsel.C	2007-04-08 07:04:03.000000000 +0200
+++ vmd-1.8.6.new/src/py_atomsel.C	2007-09-20 19:30:41.000000000 +0200
@@ -25,6 +25,10 @@
 #include "py_commands.h"
 #include "BondSearch.h"
 
+#if PY_VERSION_HEX < ((2<<24)|(5<<16))
+typedef int Py_ssize_t;
+#endif
+
 typedef struct {
   PyObject_HEAD
   AtomSel *atomSel;
@@ -915,9 +919,11 @@
  * Support for mapping protocol 
  */
 
-static int
-atomselection_length( PyAtomSelObject *a ) {
-  return a->atomSel->selected;
+
+static Py_ssize_t
+atomselection_length(PyObject *a)
+{
+  return ((PyAtomSelObject *)a)->atomSel->selected;
 }
 
 // for integer argument, return True or False if index in in selection
@@ -935,7 +941,7 @@
 }
 
 static PyMappingMethods atomsel_mapping = {
-  (inquiry)atomselection_length,
+  atomselection_length,
   (binaryfunc)atomselection_subscript,
   0
 };