diff --git a/src/trezor/wire/__init__.py b/src/trezor/wire/__init__.py
index 0431cca3..40040f63 100644
--- a/src/trezor/wire/__init__.py
+++ b/src/trezor/wire/__init__.py
@@ -12,9 +12,7 @@ from .wire_codec import \
     decode_wire_stream, encode_wire_message, \
     encode_session_open_message, encode_session_close_message
 from .wire_codec_v1 import \
-    SESSION_V1, \
-    decode_wire_v1_stream, \
-    encode_wire_v1_message
+    SESSION_V1, decode_wire_v1_stream, encode_wire_v1_message
 
 _session_handlers = {}  # session id -> generator
 _workflow_genfuncs = {}  # wire type -> (generator function, args)
@@ -138,8 +136,8 @@ async def monitor_workflow(workflow, session_id):
     finally:
         if session_id in _opened_sessions:
             if session_id == SESSION_V1:
-                wire_decoder = decode_wire_v1_stream(_handle_registered_type,
-                                                     SESSION_V1)
+                wire_decoder = decode_wire_v1_stream(
+                    _handle_registered_type, session_id)
             else:
                 wire_decoder = decode_wire_stream(
                     _handle_registered_type, session_id)
diff --git a/src/trezor/wire/wire_codec.py b/src/trezor/wire/wire_codec.py
index 1ccb8f6b..7edee032 100644
--- a/src/trezor/wire/wire_codec.py
+++ b/src/trezor/wire/wire_codec.py
@@ -83,12 +83,8 @@ Throws MessageChecksumError to target if data doesn't match the checksum.
     target.send(None)
 
     checksum = 0  # crc32
-    nreports = 1
 
     while data_len > 0:
-        if nreports > 1:
-            data_tail = memoryview((yield))  # read next report
-        nreports += 1
 
         data_chunk = data_tail[:data_len]  # slice off the garbage at the end
         data_tail = data_tail[len(data_chunk):]  # slice off what we have read
@@ -97,6 +93,9 @@ Throws MessageChecksumError to target if data doesn't match the checksum.
 
         checksum = ubinascii.crc32(data_chunk, checksum)
 
+        if data_len > 0:
+            data_tail = memoryview((yield))  # read next report
+
     msg_footer = data_tail[:_MSG_FOOTER_LEN]
     if len(msg_footer) < _MSG_FOOTER_LEN:
         data_tail = yield  # read report with the rest of checksum
@@ -137,7 +136,7 @@ def encode_wire_message(msg_type, msg_data, session_id, target):
             msg_footer = None
             continue
 
-        # FIXME: Optimize speed
+        # FIXME: optimize speed
         x = 0
         to_fill = len(target_data)
         while x < to_fill:
diff --git a/src/trezor/wire/wire_codec_v1.py b/src/trezor/wire/wire_codec_v1.py
index 384a6f58..c0c1b296 100644
--- a/src/trezor/wire/wire_codec_v1.py
+++ b/src/trezor/wire/wire_codec_v1.py
@@ -1,28 +1,36 @@
 import ustruct
 
 SESSION_V1 = const(0)
-REP_MARKER_V1 = const(63) # ord('?)
-REP_MARKER_V1_LEN = const(1) # len('?')
+REP_MARKER_V1 = const(63)  # ord('?)
+REP_MARKER_V1_LEN = const(1)  # len('?')
 
-_MSG_HEADER_MAGIC = const(35) # org('#')
-_MSG_HEADER_V1 = '>BBHL'  # wire type, data length
+_REP_LEN = const(64)
+_MSG_HEADER_MAGIC = const(35)  # org('#')
+_MSG_HEADER_V1 = '>BBHL'  # magic, magic, wire type, data length
 _MSG_HEADER_V1_LEN = ustruct.calcsize(_MSG_HEADER_V1)
 
+
 def detect_v1(data):
     return (data[0] == REP_MARKER_V1)
 
+
 def parse_report_v1(data):
     return None, SESSION_V1, data[1:]
 
+
 def parse_message(data):
     magic1, magic2, msg_type, data_len = ustruct.unpack(_MSG_HEADER_V1, data)
     if magic1 != _MSG_HEADER_MAGIC or magic2 != _MSG_HEADER_MAGIC:
-        raise Exception("Corrupted magic bytes")
+        raise Exception('Corrupted magic bytes')
 
     return msg_type, data_len, data[_MSG_HEADER_V1_LEN:]
 
+
 def serialize_message_header(data, msg_type, msg_len):
-    ustruct.pack_into(_MSG_HEADER_V1, data, REP_MARKER_V1_LEN, _MSG_HEADER_MAGIC, _MSG_HEADER_MAGIC, msg_type, msg_len)
+    ustruct.pack_into(
+        _MSG_HEADER_V1, data, REP_MARKER_V1_LEN,
+        _MSG_HEADER_MAGIC, _MSG_HEADER_MAGIC, msg_type, msg_len)
+
 
 def decode_wire_v1_stream(genfunc, session_id, *args):
     '''Decode a v1 wire message from the report data and stream it to target.
@@ -32,8 +40,8 @@ Sends (msg_type, data_len) to target, followed by data chunks.
 Throws EOFError after last data chunk, in case of valid checksum.
 Throws MessageChecksumError to target if data doesn't match the checksum.
 '''
-    
-    message = yield # read first report
+
+    message = yield  # read first report
     msg_type, data_len, data = parse_message(message)
 
     print(msg_type, data_len, bytes(data))
@@ -48,17 +56,18 @@ Throws MessageChecksumError to target if data doesn't match the checksum.
         target.send(data_chunk)
 
         if data_len > 0:
-            data = yield # First next record
+            data = yield  # read next report
 
     target.throw(EOFError())
 
+
 def encode_wire_v1_message(msg_type, msg_data, target):
-    report = memoryview(bytearray(64)) # Maximum report length
-    report[0] = REP_MARKER_V1 # Put report marker
+    report = memoryview(bytearray(_REP_LEN))
+    report[0] = REP_MARKER_V1
     serialize_message_header(report, msg_type, len(msg_data))
 
     source_data = memoryview(msg_data)
-    target_data = report[REP_MARKER_V1_LEN+_MSG_HEADER_V1_LEN:]
+    target_data = report[REP_MARKER_V1_LEN + _MSG_HEADER_V1_LEN:]
 
     while True:
         # move as much as possible from source to target
@@ -67,7 +76,7 @@ def encode_wire_v1_message(msg_type, msg_data, target):
         source_data = source_data[n:]
         target_data = target_data[n:]
 
-        # FIXME: Optimize speed
+        # FIXME: optimize speed
         x = 0
         to_fill = len(target_data)
         while x < to_fill:
@@ -79,4 +88,5 @@ def encode_wire_v1_message(msg_type, msg_data, target):
         if not source_data:
             break
 
-        target_data = report[REP_MARKER_V1_LEN:]
\ No newline at end of file
+        # reset to skip the magic, not the whole header anymore
+        target_data = report[REP_MARKER_V1_LEN:]