diff --git a/bitcoinrpc/authproxy.py b/bitcoinrpc/authproxy.py
index 7a104ff..75d637d 100644
--- a/bitcoinrpc/authproxy.py
+++ b/bitcoinrpc/authproxy.py
@@ -61,7 +61,7 @@ def __init__(self, rpc_error):
 
 def EncodeDecimal(o):
     if isinstance(o, decimal.Decimal):
-        return round(o, 8)
+        return float(round(o, 8))
     raise TypeError(repr(o) + " is not JSON serializable")
 
 class AuthServiceProxy(object):