updated for version 7.3.580
Problem:    Warning on 64 bit MS-Windows.
Solution:   Add type cast. (Mike Williams)
diff --git a/src/if_py_both.h b/src/if_py_both.h
index 8229458..0912ee0 100644
--- a/src/if_py_both.h
+++ b/src/if_py_both.h
@@ -495,7 +495,7 @@
     if (!PyArg_ParseTuple(args, "s", &expr))
 	return NULL;
 
-    return PyLong_FromLong(mb_string2cells((char_u *)expr, STRLEN(expr)));
+    return PyLong_FromLong(mb_string2cells((char_u *)expr, (int)STRLEN(expr)));
 }
 
 /*