diff --git a/umsgpack.py b/umsgpack.py
index 3094178..8ee5d77 100644
--- a/umsgpack.py
+++ b/umsgpack.py
@@ -19,10 +19,11 @@ def __init__(self, type, data):
         if not isinstance(type, int) or not (type >= 0 and type <= 127):
             raise TypeError("ext type out of range")
         # Check data is type bytes
+        elif (isinstance(sys.version_info, tuple) or
+                sys.version_info.major == 2) and not isinstance(data, str):
+            raise TypeError("ext data is not type \'str\'")
         elif sys.version_info.major == 3 and not isinstance(data, bytes):
             raise TypeError("ext data is not type \'bytes\'")
-        elif sys.version_info.major == 2 and not isinstance(data, str):
-            raise TypeError("ext data is not type \'str\'")
         self.type = type
         self.data = data
 
@@ -449,7 +450,7 @@ def __init():
         _float_size = 32
 
     # Map packb and unpackb to the appropriate version
-    if sys.version_info.major == 3:
+    if not isinstance(sys.version_info, tuple) and sys.version_info.major == 3:
         packb = packb3
         unpackb = unpackb3
     else: