diff --git a/src/lib/formats/wd177x_dsk.h b/src/lib/formats/wd177x_dsk.h
index 966e790d5d8..0237bb9989c 100644
--- a/src/lib/formats/wd177x_dsk.h
+++ b/src/lib/formats/wd177x_dsk.h
@@ -42,8 +42,8 @@ public:
 
 protected:
 	const format *formats;
-	floppy_image_format_t::desc_e* get_desc_fm(const format &f, int &current_size, int &end_gap_index);
-	floppy_image_format_t::desc_e* get_desc_mfm(const format &f, int &current_size, int &end_gap_index);
+	virtual floppy_image_format_t::desc_e* get_desc_fm(const format &f, int &current_size, int &end_gap_index);
+	virtual floppy_image_format_t::desc_e* get_desc_mfm(const format &f, int &current_size, int &end_gap_index);
 	int find_size(io_generic *io, UINT32 form_factor);
 	int compute_track_size(const format &f) const;
 	void build_sector_description(const format &d, UINT8 *sectdata, desc_s *sectors) const;
diff --git a/src/mess/drivers/xerox820.c b/src/mess/drivers/xerox820.c
index f218a278893..15678e36234 100644
--- a/src/mess/drivers/xerox820.c
+++ b/src/mess/drivers/xerox820.c
@@ -13,7 +13,9 @@
     TODO:
 
     - Xerox 820
-        - floppy (wd1772.c FM support)
+        - floppy format has 3xcd at the end of track data
+	        :u109: write track 0
+			:u109: track description 16xff ... 109xff 3xcd
     - Xerox 820-II
         - floppy (read/write to FDC triggers Z80 WAIT)
         - Winchester