diff --git a/python/cspdylay.pxd b/python/cspdylay.pxd
index 282d6060..c0579e0b 100644
--- a/python/cspdylay.pxd
+++ b/python/cspdylay.pxd
@@ -23,6 +23,10 @@ cdef extern from 'spdylay/spdylay.h':
         SPDYLAY_CTRL_FLAG_FIN
         SPDYLAY_CTRL_FLAG_UNIDIRECTIONAL
 
+    ctypedef enum spdylay_data_flag:
+        SPDYLAY_DATA_FLAG_NONE
+        SPDYLAY_DATA_FLAG_FIN
+
     ctypedef enum spdylay_frame_type:
         SPDYLAY_SYN_STREAM
         SPDYLAY_SYN_REPLY
diff --git a/python/spdylay.pyx b/python/spdylay.pyx
index d00be6c0..e16bf5f9 100644
--- a/python/spdylay.pyx
+++ b/python/spdylay.pyx
@@ -303,10 +303,10 @@ cdef ssize_t send_callback(cspdylay.spdylay_session *session,
             pysession.base_error = e
             return cspdylay.SPDYLAY_ERR_CALLBACK_FAILURE
 
-        if rv == cspdylay.SPDYLAY_ERR_WOULDBLOCK:
-            return cspdylay.SPDYLAY_ERR_WOULDBLOCK
-        else:
+        if rv:
             return rv
+        else:
+            return cspdylay.SPDYLAY_ERR_WOULDBLOCK
     else:
         # If no send_callback is given, pretend all data were sent and
         # just return length
@@ -402,9 +402,9 @@ cdef class Session:
             return self.user_data
 
     def __cinit__(self, side, version,
-                  recv_cb=None, send_cb=None,
-                  on_data_chunk_recv_cb=None,
+                  send_cb=None, recv_cb=None,
                   on_ctrl_recv_cb=None,
+                  on_data_chunk_recv_cb=None,
                   on_stream_close_cb=None,
                   on_request_recv_cb=None,
                   user_data=None):
@@ -469,9 +469,9 @@ cdef class Session:
             raise UnsupportedVersionError(cspdylay.spdylay_strerror(rv))
 
     def __init__(self, side, version,
-                 recv_cb=None, send_cb=None,
-                 on_data_chunk_recv_cb=None,
+                 send_cb=None, recv_cb=None,
                  on_ctrl_recv_cb=None,
+                 on_data_chunk_recv_cb=None,
                  on_stream_close_cb=None,
                  on_request_recv_cb=None,
                  user_data=None):
@@ -686,6 +686,10 @@ CTRL_FLAG_NONE = cspdylay.SPDYLAY_CTRL_FLAG_NONE
 CTRL_FLAG_FIN = cspdylay.SPDYLAY_CTRL_FLAG_FIN
 CTRL_FLAG_UNIDIRECTIONAL = cspdylay.SPDYLAY_CTRL_FLAG_UNIDIRECTIONAL
 
+# Data frame flags
+DATA_FLAG_NONE = cspdylay.SPDYLAY_DATA_FLAG_NONE
+DATA_FLAG_FIN = cspdylay.SPDYLAY_DATA_FLAG_FIN
+
 # Error codes used in callback
 ERR_OK = 0 # Not defined in <spdylay/spdylay.h>
 ERR_EOF = cspdylay.SPDYLAY_ERR_EOF