diff --git a/Objects/stringobject.c b/Objects/stringobject.c
index 92bc95b..62955b9 100644
--- a/Objects/stringobject.c
+++ b/Objects/stringobject.c
@@ -3265,7 +3265,7 @@
 {
     const char *e, *p;
     char *q;
-    Py_ssize_t i, j;
+    Py_ssize_t i, j, old_j;
     PyObject *u;
     int tabsize = 8;
 
@@ -3273,21 +3273,38 @@
 	return NULL;
 
     /* First pass: determine size of output string */
-    i = j = 0;
+    i = j = old_j = 0;
     e = PyString_AS_STRING(self) + PyString_GET_SIZE(self);
     for (p = PyString_AS_STRING(self); p < e; p++)
         if (*p == '\t') {
-	    if (tabsize > 0)
+	    if (tabsize > 0) {
 		j += tabsize - (j % tabsize);
+		if (old_j > j) {
+		    PyErr_SetString(PyExc_OverflowError,
+				    "new string is too long");
+		    return NULL;
+		}
+		old_j = j;
+            }
 	}
         else {
             j++;
             if (*p == '\n' || *p == '\r') {
                 i += j;
-                j = 0;
+                old_j = j = 0;
+                if (i < 0) {
+                    PyErr_SetString(PyExc_OverflowError,
+                                    "new string is too long");
+                    return NULL;
+                }
             }
         }
 
+    if ((i + j) < 0) {
+        PyErr_SetString(PyExc_OverflowError, "new string is too long");
+        return NULL;
+    }
+
     /* Second pass: create output string and fill it */
     u = PyString_FromStringAndSize(NULL, i + j);
     if (!u)
@@ -4199,12 +4216,13 @@
 		result = val->ob_type->tp_str(val);
 		break;
 	case 'o':
-		result = val->ob_type->tp_as_number->nb_oct(val);
+		numnondigits = 2;
+		result = PyNumber_ToBase(val, 8);
 		break;
 	case 'x':
 	case 'X':
 		numnondigits = 2;
-		result = val->ob_type->tp_as_number->nb_hex(val);
+		result = PyNumber_ToBase(val, 16);
 		break;
 	default:
 		assert(!"'type' not in [duoxX]");
@@ -4239,32 +4257,16 @@
 	assert(numdigits > 0);
 
 	/* Get rid of base marker unless F_ALT */
-	if ((flags & F_ALT) == 0) {
-		/* Need to skip 0x, 0X or 0. */
-		int skipped = 0;
-		switch (type) {
-		case 'o':
-			assert(buf[sign] == '0');
-			/* If 0 is only digit, leave it alone. */
-			if (numdigits > 1) {
-				skipped = 1;
-				--numdigits;
-			}
-			break;
-		case 'x':
-		case 'X':
-			assert(buf[sign] == '0');
-			assert(buf[sign + 1] == 'x');
-			skipped = 2;
-			numnondigits -= 2;
-			break;
-		}
-		if (skipped) {
-			buf += skipped;
-			len -= skipped;
-			if (sign)
-				buf[0] = '-';
-		}
+	if (((flags & F_ALT) == 0 &&
+	    (type == 'o' || type == 'x' || type == 'X'))) {
+		assert(buf[sign] == '0');
+		assert(buf[sign+1] == 'x' || buf[sign+1] == 'X' ||
+                       buf[sign+1] == 'o');
+		numnondigits -= 2;
+		buf += 2;
+		len -= 2;
+		if (sign)
+			buf[0] = '-';
 		assert(len == numnondigits + numdigits);
 		assert(numdigits > 0);
 	}
@@ -4333,9 +4335,10 @@
 		prec = 1;
 
 	if ((flags & F_ALT) &&
-	    (type == 'x' || type == 'X')) {
-		/* When converting under %#x or %#X, there are a number
+	    (type == 'x' || type == 'X' || type == 'o')) {
+		/* When converting under %#o, %#x or %#X, there are a number
 		 * of issues that cause pain:
+		 * - for %#o, we want a different base marker than C
 		 * - when 0 is being converted, the C standard leaves off
 		 *   the '0x' or '0X', which is inconsistent with other
 		 *   %#x/%#X conversions and inconsistent with Python's
@@ -4363,7 +4366,7 @@
 			      prec, type);
 	}
 
-	/* buf = '+'/'-'/'' + '0'/'0x'/'' + '[0-9]'*max(prec, len(x in octal))
+	/* buf = '+'/'-'/'' + '0o'/'0x'/'' + '[0-9]'*max(prec, len(x in octal))
 	 * worst case buf = '-0x' + [0-9]*prec, where prec >= 11
 	 */
 	if (buflen <= 14 || buflen <= (size_t)3 + (size_t)prec) {
@@ -4751,7 +4754,8 @@
 				if (width > len)
 					width--;
 			}
-			if ((flags & F_ALT) && (c == 'x' || c == 'X')) {
+			if ((flags & F_ALT) &&
+			    (c == 'x' || c == 'X' || c == 'o')) {
 				assert(pbuf[0] == '0');
 				assert(pbuf[1] == c);
 				if (fill != ' ') {
@@ -4774,7 +4778,7 @@
 				if (sign)
 					*res++ = sign;
 				if ((flags & F_ALT) &&
-				    (c == 'x' || c == 'X')) {
+				    (c == 'x' || c == 'X' || c == 'o')) {
 					assert(pbuf[0] == '0');
 					assert(pbuf[1] == c);
 					*res++ = *pbuf++;