diff --git a/tcutils/pbocfunc.py b/tcutils/pbocfunc.py
index 942ea18..7c4fe90 100644
--- a/tcutils/pbocfunc.py
+++ b/tcutils/pbocfunc.py
@@ -150,15 +150,19 @@
     offset = 0
     while offset < datalen:
         t = ord(data[offset])
-        if t & 0x0F == 0x0F:
+        if t & 0x0F == 0x0F and (t not in (0x4f, 0x8f)):
             tag = data[offset:offset + 2]
             offset += 2
         else:
             tag = data[offset]
             offset += 1
+        if offset >= datalen:
+            raise ValueError(u"data length error, cannot get tag length")
         t = ord(data[offset])
         if t & 0x80 == 0x80:
             vl = t & 0x7F
+            if offset + 1 + vl >= datalen:
+                raise ValueError(u"data length error, cannot get tag length")
             vlen = 0
             for c in data[offset + 1:offset + 1 + vl]:
                 vlen = (vlen << 8) + ord(c)
@@ -168,8 +172,8 @@
             offset += 1
 
         if datalen - offset < vlen:
-            raise ValueError(u"data length Error, tag [%s]length[%d]" % (
-                codecs.encode(tag, 'hex'), vlen))
+            raise ValueError(u"data length Error, tag [%s]length[%d],left[%d]" % (
+                codecs.encode(tag, 'hex'), vlen, datalen - offset))
         value = data[offset:offset + vlen]
         offset += vlen
         yield (tag, value,)