diff -r 6a599249e8b7 Lib/aifc.py
--- a/Lib/aifc.py	Sat Nov 16 13:04:00 2013 +0200
+++ b/Lib/aifc.py	Sat Nov 16 13:42:42 2013 +0200
@@ -788,7 +788,10 @@
                 self._datalength = (self._datalength + 3) // 4
                 if self._datalength & 1:
                     self._datalength = self._datalength + 1
-        self._form_length_pos = self._file.tell()
+        try:
+            self._form_length_pos = self._file.tell()
+        except (AttributeError, OSError):
+            self._form_length_pos = None
         commlength = self._write_form_length(self._datalength)
         if self._aifc:
             self._file.write(b'AIFC')
@@ -800,7 +803,8 @@
         self._file.write(b'COMM')
         _write_ulong(self._file, commlength)
         _write_short(self._file, self._nchannels)
-        self._nframes_pos = self._file.tell()
+        if self._form_length_pos is not None:
+            self._nframes_pos = self._file.tell()
         _write_ulong(self._file, self._nframes)
         if self._comptype in (b'ULAW', b'ulaw', b'ALAW', b'alaw', b'G722'):
             _write_short(self._file, 8)
@@ -811,7 +815,8 @@
             self._file.write(self._comptype)
             _write_string(self._file, self._compname)
         self._file.write(b'SSND')
-        self._ssnd_length_pos = self._file.tell()
+        if self._form_length_pos is not None:
+            self._ssnd_length_pos = self._file.tell()
         _write_ulong(self._file, self._datalength + 8)
         _write_ulong(self._file, 0)
         _write_ulong(self._file, 0)
diff -r 6a599249e8b7 Lib/test/test_aifc.py
--- a/Lib/test/test_aifc.py	Sat Nov 16 13:04:00 2013 +0200
+++ b/Lib/test/test_aifc.py	Sat Nov 16 13:42:42 2013 +0200
@@ -13,9 +13,6 @@
     module = aifc
     close_fd = True
     test_unseekable_read = None
-    test_unseekable_write = None
-    test_unseekable_incompleted_write = None
-    test_unseekable_overflowed_write = None
 
 
 class AifcPCM8Test(AifcTest, unittest.TestCase):