diff --git a/libtiff/tif_fax3.c b/libtiff/tif_fax3.c
index 5ad52254..4809eabf 100644
--- a/libtiff/tif_fax3.c
+++ b/libtiff/tif_fax3.c
@@ -1453,8 +1453,13 @@ Fax4Decode(TIFF* tif, uint8* buf, tmsize_t occ, uint16 s)
 		EXPAND2D(EOFG4);
                 if (EOLcnt)
                     goto EOFG4;
-		if (((lastx + 7) >> 3) > (int)occ)	/* check for buffer overflow */
+		if (((lastx + 7) >> 3) > (int)occ)	/* check for buffer overrun */
+		{
+			TIFFErrorExt(tif->tif_clientdata, module,
+			             "Buffer overrun detected : %d bytes available, %d bits needed",
+			             (int)occ, lastx);
 			return -1;
+		}
 		(*sp->fill)(buf, thisrun, pa, lastx);
 		SETVALUE(0);		/* imaginary change for reference */
 		SWAP(uint32*, sp->curruns, sp->refruns);
@@ -1470,8 +1475,13 @@ Fax4Decode(TIFF* tif, uint8* buf, tmsize_t occ, uint16 s)
                     fputs( "Bad EOFB\n", stderr );
 #endif                
                 ClrBits( 13 );
-		if (((lastx + 7) >> 3) > (int)occ)	/* check for buffer overflow */
+		if (((lastx + 7) >> 3) > (int)occ)	/* check for buffer overrun */
+		{
+			TIFFErrorExt(tif->tif_clientdata, module,
+			             "Buffer overrun detected : %d bytes available, %d bits needed",
+			             (int)occ, lastx);
 			return -1;
+		}
 		(*sp->fill)(buf, thisrun, pa, lastx);
 		UNCACHE_STATE(tif, sp);
 		return ( sp->line ? 1 : -1);	/* don't error on badly-terminated strips */