diff -r f97630b6ebd8 Objects/stringlib/transmogrify.h
--- a/Objects/stringlib/transmogrify.h	Tue Jan 13 03:11:23 2009 +0100
+++ b/Objects/stringlib/transmogrify.h	Tue Jan 13 20:56:20 2009 +0100
@@ -22,7 +22,7 @@ stringlib_expandtabs(PyObject *self, PyO
 {
     const char *e, *p;
     char *q;
-    Py_ssize_t i, j, old_j;
+    size_t i, j, old_i, old_j;
     PyObject *u;
     int tabsize = 8;
 
@@ -30,15 +30,13 @@ stringlib_expandtabs(PyObject *self, PyO
 	return NULL;
 
     /* First pass: determine size of output string */
-    i = j = old_j = 0;
+    i = j = old_i = old_j = 0;
     e = STRINGLIB_STR(self) + STRINGLIB_LEN(self);
     for (p = STRINGLIB_STR(self); p < e; p++)
         if (*p == '\t') {
 	    if (tabsize > 0) {
 		j += tabsize - (j % tabsize);
-                /* XXX: this depends on a signed integer overflow to < 0 */
-                /* C compilers, including gcc, do -NOT- guarantee this. */
-		if (old_j > j) {
+		if (j > PY_SSIZE_T_MAX) {
 		    PyErr_SetString(PyExc_OverflowError,
 				    "result is too long");
 		    return NULL;
@@ -51,19 +49,16 @@ stringlib_expandtabs(PyObject *self, PyO
             if (*p == '\n' || *p == '\r') {
                 i += j;
                 old_j = j = 0;
-                /* XXX: this depends on a signed integer overflow to < 0 */
-                /* C compilers, including gcc, do -NOT- guarantee this. */
-                if (i < 0) {
+                if (i > PY_SSIZE_T_MAX) {
                     PyErr_SetString(PyExc_OverflowError,
                                     "result is too long");
                     return NULL;
                 }
+                old_i = i;
             }
         }
 
-    if ((i + j) < 0) {
-        /* XXX: this depends on a signed integer overflow to < 0 */
-        /* C compilers, including gcc, do -NOT- guarantee this. */
+    if ((i + j) > PY_SSIZE_T_MAX) {
         PyErr_SetString(PyExc_OverflowError, "result is too long");
         return NULL;
     }