diff --git a/SWIG/Lib/python/pyhead.swg b/SWIG/Lib/python/pyhead.swg
index c9534a6ae..8451337e3 100644
--- a/SWIG/Lib/python/pyhead.swg
+++ b/SWIG/Lib/python/pyhead.swg
@@ -4,7 +4,7 @@
 /* Add PyOS_snprintf for old Pythons */
 #if PY_VERSION_HEX < 0x02020000
 # if defined(_MSC_VER) || defined(__BORLANDC__) || defined(_WATCOM)
-#   define PyOS_snprintf _snprintf
+#  define PyOS_snprintf _snprintf
 # else
 #  define PyOS_snprintf snprintf
 # endif
@@ -14,7 +14,7 @@
 #if PY_VERSION_HEX < 0x02020000
 
 #ifndef SWIG_PYBUFFER_SIZE
-#define SWIG_PYBUFFER_SIZE 1024
+# define SWIG_PYBUFFER_SIZE 1024
 #endif
 
 static PyObject *
@@ -25,32 +25,46 @@ PyString_FromFormat(const char *fmt, ...) {
   va_start(ap, fmt);
   res = vsnprintf(buf, sizeof(buf), fmt, ap);
   va_end(ap);
-  return (res < 0 || res >= sizeof(buf)) ? 0 : PyString_FromString(buf);
+  return (res < 0 || res >= (int)sizeof(buf)) ? 0 : PyString_FromString(buf);
 }
 #endif
 
 /* Add PyObject_Del for old Pythons */
 #if PY_VERSION_HEX < 0x01060000
-#define PyObject_Del(op) PyMem_DEL((op))
+# define PyObject_Del(op) PyMem_DEL((op))
 #endif
 #ifndef PyObject_DEL
-#define PyObject_DEL PyObject_Del
+# define PyObject_DEL PyObject_Del
 #endif
 
 /* A crude PyExc_StopIteration exception for old Pythons */
 #if PY_VERSION_HEX < 0x02020000
-#define PyExc_StopIteration PyExc_RuntimeError
-#define PyObject_GenericGetAttr 0
-#define Py_NotImplemented PyExc_RuntimeError
+# ifndef PyExc_StopIteration
+#  define PyExc_StopIteration PyExc_RuntimeError
+# endif
+# ifndef PyObject_GenericGetAttr
+#  define PyObject_GenericGetAttr 0
+# endif
+#endif
+/* Py_NotImplemented is defined in 2.1 and up. */
+#if PY_VERSION_HEX < 0x02010000
+# ifndef Py_NotImplemented
+#  define Py_NotImplemented PyExc_RuntimeError
+# endif
 #endif
 
 
 /* A crude PyString_AsStringAndSize implementation for old Pythons */
 #if PY_VERSION_HEX < 0x02010000
-#define PyString_AsStringAndSize(obj, s, len) {*s = PyString_AsString(obj); *len = *s ? strlen(*s) : 0;}
+# ifndef PyString_AsStringAndSize
+#  define PyString_AsStringAndSize(obj, s, len) {*s = PyString_AsString(obj); *len = *s ? strlen(*s) : 0;}
+# endif
 #endif
 
+/* PySequence_Size for old Pythons */
 #if PY_VERSION_HEX < 0x02000000
-#define PySequence_Size PySequence_Length
+# ifndef PySequence_Size
+#  define PySequence_Size PySequence_Length
+# endif
 #endif