Index: Python/mystrtoul.c
===================================================================
--- Python/mystrtoul.c	(revision 60075)
+++ Python/mystrtoul.c	(working copy)
@@ -110,29 +110,34 @@
 	while (*str && isspace(Py_CHARMASK(*str)))
 		++str;
 
-	/* check for leading 0 or 0x for auto-base or base 16 */
-	switch (base) {
-		case 0:		/* look for leading 0, 0x or 0X */
-			if (*str == '0') {
-				++str;
-				if (*str == 'x' || *str == 'X') {
-					++str;
-					base = 16;
-				}
-				else
-					base = 8;
+	/* handle auto-base */
+	if (base == 0) {
+		if(*str == '0') {
+			if (str[1] == 'x' || str[1] == 'X') {
+				base = 16;
+			} else {
+				base = 8;
 			}
-			else
-				base = 10;
-			break;
+		} else {
+			base = 10;
+		}
+	}
 
-		case 16:	/* skip leading 0x or 0X */
-			if (*str == '0') {
+	/* check for leading 0x for base 16 */
+	if (base == 16 && *str == '0') {
+		++str;
+		/* If 0x is followed by a digit, gobble it.
+		   Otherwise, "0x" is not a valid int literal, but 0 is,
+		   so only gobble the 0 and return 0. */
+		if (*str == 'x' || *str == 'X') {
+			if (_PyLong_DigitValue[Py_CHARMASK(str[1])] < base) {
 				++str;
-				if (*str == 'x' || *str == 'X')
-					++str;
+			} else {
+				if(ptr)
+					*ptr = str;
+				return 0;
 			}
-			break;
+		}
 	}
 
 	/* catch silly bases */