Fix a couple of warnings on Mac OS X.
diff --git a/Mac/Modules/Nav.c b/Mac/Modules/Nav.c
index 0041f76..6786ea0 100644
--- a/Mac/Modules/Nav.c
+++ b/Mac/Modules/Nav.c
@@ -131,7 +131,7 @@
 		OSType *fileTypeP,
 		OSType *fileCreatorP)
 {
-	int pos = 0;
+	Py_ssize_t pos = 0;
 	PyObject *key, *value;
 	char *keystr;
 	AEDesc *defaultLocation_storage;
diff --git a/Mac/Modules/cf/pycfbridge.c b/Mac/Modules/cf/pycfbridge.c
index 30122dc..ae9e128 100644
--- a/Mac/Modules/cf/pycfbridge.c
+++ b/Mac/Modules/cf/pycfbridge.c
@@ -283,7 +283,7 @@
 	
 	if (PyString_Check(src)) {
 		if (!PyArg_Parse(src, "es", "ascii", &chars))
-			return NULL; /* This error is more descriptive than the general one below */
+			return 0; /* This error is more descriptive than the general one below */
 		*dst = CFStringCreateWithCString((CFAllocatorRef)NULL, chars, kCFStringEncodingASCII);
 		return 1;
 	}