Index: Lib/wave.py
===================================================================
--- Lib/wave.py	(revision 68230)
+++ Lib/wave.py	(working copy)
@@ -146,7 +146,8 @@
                 if not self._fmt_chunk_read:
                     raise Error, 'data chunk before fmt chunk'
                 self._data_chunk = chunk
-                self._nframes = chunk.chunksize // self._framesize
+                self._nframes = (chunk.chunksize // (
+                    self._framesize * self._sampwidth))
                 self._data_seek_needed = 0
                 break
             chunk.skip()
@@ -421,22 +422,19 @@
             data = array.array(_array_fmts[self._sampwidth], data)
             data.byteswap()
             data.tofile(self._file)
-            self._datawritten = self._datawritten + len(data) * self._sampwidth
         else:
             self._file.write(data)
-            self._datawritten = self._datawritten + len(data)
+        self._datawritten = self._datawritten + len(data) * self._sampwidth
         self._nframeswritten = self._nframeswritten + nframes
 
     def writeframes(self, data):
         self.writeframesraw(data)
-        if self._datalength != self._datawritten:
-            self._patchheader()
+        self._patchheader()
 
     def close(self):
         if self._file:
             self._ensure_header_written(0)
-            if self._datalength != self._datawritten:
-                self._patchheader()
+            self._patchheader()
             self._file.flush()
             self._file = None
         if self._i_opened_the_file: