diff --git a/amodem/dsp.py b/amodem/dsp.py
index 1626e9b..e2f5fb9 100644
--- a/amodem/dsp.py
+++ b/amodem/dsp.py
@@ -130,7 +130,7 @@ class MODEM(object):
         self.symbols = symbols
         self.bits_per_symbol = bits_per_symbol
 
-        bits_map = {symbol: bits for bits, symbol in self.encode_map.items()}
+        bits_map = dict((symbol, bits) for bits, symbol in self.encode_map.items())
         self.decode_list = [(s, bits_map[s]) for s in self.symbols]
 
     def encode(self, bits):