diff --git a/Lib/pickle.py b/Lib/pickle.py
index dffdc2c..6045c84 100644
--- a/Lib/pickle.py
+++ b/Lib/pickle.py
@@ -158,6 +158,9 @@
 
 _quotes = ["'", '"']
 
+
+# Pickling machinery
+
 class Pickler:
 
     def __init__(self, file, proto=1):
@@ -178,11 +181,11 @@
         object, or any other custom object that meets this interface.
 
         """
-        if not 0 <= proto <= 2:
+        if proto not in (0, 1, 2):
             raise ValueError, "pickle protocol must be 0, 1 or 2"
         self.write = file.write
         self.memo = {}
-        self.proto = proto
+        self.proto = int(proto)
         self.bin = proto >= 1
 
     def clear_memo(self):
@@ -639,6 +642,7 @@
     dispatch[BuiltinFunctionType] = save_global
     dispatch[TypeType] = save_global
 
+# Pickling helpers
 
 def _keep_alive(x, memo):
     """Keeps a reference to the object x in the memo.
@@ -683,6 +687,8 @@
     return name
 
 
+# Unpickling machinery
+
 class Unpickler:
 
     def __init__(self, file):