diff --git a/msgpack/_packer.pyx b/msgpack/_packer.pyx
index a4913ab7..35e5a9dc 100644
--- a/msgpack/_packer.pyx
+++ b/msgpack/_packer.pyx
@@ -289,11 +289,13 @@ cdef class Packer(object):
 
     cpdef pack(self, object obj):
         cdef int ret
-        ret = self._pack(obj, DEFAULT_RECURSE_LIMIT)
-        if ret == -1:
-            raise MemoryError
-        elif ret:  # should not happen.
-            raise TypeError
+        try:
+            ret = self._pack(obj, DEFAULT_RECURSE_LIMIT)
+        except:
+            self.pk.length = 0
+            raise
+        if ret:  # should not happen.
+            raise RuntimeError("internal error")
         if self.autoreset:
             buf = PyBytes_FromStringAndSize(self.pk.buf, self.pk.length)
             self.pk.length = 0
diff --git a/msgpack/fallback.py b/msgpack/fallback.py
index d95f6218..675ee8a5 100644
--- a/msgpack/fallback.py
+++ b/msgpack/fallback.py
@@ -848,7 +848,11 @@ def _pack(self, obj, nest_limit=DEFAULT_RECURSE_LIMIT,
             raise TypeError("Cannot serialize %r" % (obj, ))
 
     def pack(self, obj):
-        self._pack(obj)
+        try:
+            self._pack(obj)
+        except:
+            self._buffer = StringIO()  # force reset
+            raise
         ret = self._buffer.getvalue()
         if self._autoreset:
             self._buffer = StringIO()