Index: osl/unx/file.cxx
===================================================================
--- osl/unx/file.cxx	(revision 276042)
+++ osl/unx/file.cxx	(working copy)
@@ -110,6 +110,7 @@
     oslFileError setPos (sal_uInt64 uPos);
 
     sal_uInt64   getSize() const;
+    void         setSize( sal_uInt64 nSize );
 
     oslFileError readAt (
         off_t        nOffset,
@@ -271,6 +272,23 @@
     return std::max(m_size, sal::static_int_cast< sal_uInt64 >(bufend));
 }
 
+void FileHandle_Impl::setSize( sal_uInt64 nSize )
+{
+    if ( nSize < sal::static_int_cast< sal_uInt64 >( m_bufptr ) )
+    {
+        m_bufptr = 0;
+        m_buflen = 0;
+    }
+    else
+    {
+        off_t const bufend = std::max((off_t)(0), m_bufptr) + m_buflen;
+        if ( nSize < sal::static_int_cast< sal_uInt64 >( bufend ) )
+            m_buflen = sal::static_int_cast< off_t >( nSize - sal::static_int_cast< sal_uInt64 >( m_bufptr ) );
+    }
+
+    m_size = nSize;
+}
+
 oslFileError FileHandle_Impl::readAt (
     off_t        nOffset,
     void *       pBuffer,
@@ -1338,6 +1356,7 @@
 	}
 
     OSL_FILE_TRACE("osl_setFileSize(%d, %lld) => %ld", pImpl->m_fd, pImpl->getSize(), nSize);
-    pImpl->m_size = sal::static_int_cast< sal_uInt64 >(nSize);
+    pImpl->setSize( uSize );
+
 	return osl_File_E_None;
 }
Index: osl/w32/file.cxx
===================================================================
--- osl/w32/file.cxx	(revision 276042)
+++ osl/w32/file.cxx	(working copy)
@@ -103,6 +103,7 @@
 	oslFileError  setPos (sal_uInt64 uPos);
 
 	sal_uInt64    getSize() const;
+	void          setSize( sal_uInt64 );
 
 	oslFileError readAt (
 		LONGLONG     nOffset,
@@ -253,6 +254,24 @@
 	return std::max(m_size, sal::static_int_cast< sal_uInt64 >(bufend));
 }
 
+void FileHandle_Impl::setSize( sal_uInt64 nSize )
+{
+    if ( nSize < sal::static_int_cast< sal_uInt64 >( m_bufptr ) )
+    {
+        m_bufptr = 0;
+        m_buflen = 0;
+    }
+    else
+    {
+        LONGLONG const bufend = std::max((LONGLONG)(0), m_bufptr) + m_buflen;
+        if ( nSize < sal::static_int_cast< sal_uInt64 >( bufend ) )
+            m_buflen = sal::static_int_cast< SIZE_T >( nSize - sal::static_int_cast< sal_uInt64 >( m_bufptr ) );
+    }
+
+    m_size = nSize;
+}
+
+
 oslFileError FileHandle_Impl::readAt (
 	LONGLONG     nOffset,
 	void *       pBuffer,
@@ -1056,7 +1075,7 @@
 
 	if (!::SetEndOfFile(pImpl->m_hFile))
 		return oslTranslateFileError( GetLastError() );
-	pImpl->m_size = uSize;
+	pImpl->setSize( uSize );
 
 	nDstPos.QuadPart = pImpl->m_offset;
 	if (!::SetFilePointerEx(pImpl->m_hFile, nDstPos, 0, FILE_BEGIN))