--- libsndfile-1.0.28/src/rf64.c	2017-04-02 09:43:22.000000000 +0200

+++ libsndfile-1.0.27/src/rf64.c	2016-04-01 23:08:53.000000000 +0200

@@ -735,25 +734,27 @@ rf64_write_header (SF_PRIVATE *psf, int

 #endif

-	pad_size = psf->dataoffset - 16 - psf->header.indx ;

-	if (pad_size >= 0)

-		psf_binheader_writef (psf, "m4z", PAD_MARKER, pad_size, make_size_t (pad_size)) ;

+	if (psf->header.indx + 8 < psf->dataoffset)

+	{	/* Add PAD data if necessary. */

+		int k = psf->dataoffset - 16 - psf->header.indx ;

+		psf_binheader_writef (psf, "m4z", PAD_MARKER, k, make_size_t (k)) ;

+		} ;

 	if (wpriv->rf64_downgrade && (psf->filelength < RIFF_DOWNGRADE_BYTES))

 		psf_binheader_writef (psf, "tm8", data_MARKER, psf->datalength) ;

 	else

 		psf_binheader_writef (psf, "m4", data_MARKER, 0xffffffff) ;

-	psf_fwrite (psf->header.ptr, psf->header.indx, 1, psf) ;

+	psf_fwrite (psf->header.ptr, psf->header.indx, 1, psf) ;

 	if (psf->error)

 		return psf->error ;

-	if (has_data && psf->dataoffset != psf->header.indx)

-	{	psf_log_printf (psf, "Oooops : has_data && psf->dataoffset != psf->header.indx\n") ;

+	if (has_data && psf->dataoffset != psf->header.indx)

+	{	psf_log_printf (psf, "Oooops : has_data && psf->dataoffset != psf->header.indx\n") ;

 		return psf->error = SFE_INTERNAL ;

 		} ;

-	psf->dataoffset = psf->header.indx ;

+	psf->dataoffset = psf->header.indx ;

 	if (NOT (has_data))

 		psf_fseek (psf, psf->dataoffset, SEEK_SET) ;