diff --git a/spec/tags/core/string/to_i_tags.txt b/spec/tags/core/string/to_i_tags.txt
index 9172abba8..dbec10fe9 100644
--- a/spec/tags/core/string/to_i_tags.txt
+++ b/spec/tags/core/string/to_i_tags.txt
@@ -1,8 +1 @@
 fails:String#to_i interprets leading characters as a number in the given base
-fails:String#to_i auto-detects base 8 via leading 0 when base = 0
-fails:String#to_i auto-detects base 2 via 0b when base = 0
-fails:String#to_i auto-detects base 10 via 0d when base = 0
-fails:String#to_i auto-detects base 8 via 0o when base = 0
-fails:String#to_i auto-detects base 16 via 0x when base = 0
-fails:String#to_i auto-detects base 10 with no base specifier when base = 0
-fails:String#to_i doesn't handle foreign base specifiers when base is > 0
diff --git a/topaz/objects/stringobject.py b/topaz/objects/stringobject.py
index c38161bab..344755758 100644
--- a/topaz/objects/stringobject.py
+++ b/topaz/objects/stringobject.py
@@ -10,11 +10,14 @@
 from rpython.rlib.rsre import rsre_core
 from rpython.rlib.rstring import split
 
+from topaz.coerce import Coerce
 from topaz.module import ClassDef, check_frozen
 from topaz.modules.comparable import Comparable
 from topaz.objects.objectobject import W_Object
 from topaz.utils.formatting import StringFormatter
 
+RADIX_MAP = {"x": 16, "d": 10, "b": 2, "o": 8, "X": 16, "D": 10, "B": 2, "O": 8}
+
 
 def create_trans_table(source, replacement, inv=False):
     src = expand_trans_str(source, len(source), inv)
@@ -775,19 +778,39 @@ def to_bigint(self, s, neg, i, radix):
             val = val.neg()
         return val
 
-    @classdef.method("to_i", radix="int")
-    def method_to_i(self, space, radix=10):
-        if not 2 <= radix <= 36:
-            raise space.error(space.w_ArgumentError, "invalid radix %d" % radix)
+    @classdef.method("to_i")
+    def method_to_i(self, space, w_radix=None):
+        if w_radix is None:
+            is_radix = False
+            radix = 10
+        else:
+            is_radix = True
+            radix = Coerce.int(space, w_radix)
         s = space.str_w(self)
         i = 0
-        while i < len(s):
+        length = len(s)
+        while i < length:
             if not s[i].isspace():
                 break
             i += 1
-        neg = i < len(s) and s[i] == "-"
+        neg = i < length and s[i] == "-"
         if neg:
             i += 1
+        if i < length and s[i] == "0":
+            if i + 1 < length:
+                try:
+                    r = RADIX_MAP[s[i + 1]]
+                except KeyError:
+                    if radix == 0:
+                        radix = 8
+                else:
+                    if not is_radix or radix == r or radix == 0:
+                        radix = r
+                        i += 2
+        if radix == 0:
+            radix = 10
+        if not 2 <= radix <= 36:
+            raise space.error(space.w_ArgumentError, "invalid radix %d" % radix)
         try:
             value = self.to_int(s, neg, i, radix)
         except OverflowError: