diff --git a/graphics/hgr/boxes/fast_test.s b/graphics/hgr/boxes/fast_test.s
index 61117c35..f87f5ada 100644
--- a/graphics/hgr/boxes/fast_test.s
+++ b/graphics/hgr/boxes/fast_test.s
@@ -6,6 +6,7 @@ GBASL	= $26
 GBASH	= $27
 
 
+OTHER_MASK = $73
 XRUN	= $74
 COUNT	= $75
 
@@ -141,7 +142,41 @@ simple_rectangle_loop:
 	lda	HGR_BITS
 	jsr	COLOR_SHIFT
 
-	; check if narrow case where in same
+no_shift:
+
+	; check if narrow corner case where begin and end same block
+	; if RX%7 + XRUN > 8
+
+	ldx	VGI_RX1
+	lda	mod7_table,X
+	clc
+	adc	XRUN
+	cmp	#8
+	bcs	not_corner
+
+;	jmp	not_corner
+
+corner:
+	; want to use MASK of left_mask, MOD7 and 7-XRUN
+
+	lda	#7
+	sec
+	sbc	XRUN
+	sta	OTHER_MASK
+
+	lda	mod7_table,X
+	tax
+
+	lda	(GBASL),Y
+	eor	HGR_BITS
+	and	left_masks,X
+	and	OTHER_MASK
+	eor	(GBASL),Y
+	sta	(GBASL),Y
+
+	jmp	done_row
+
+not_corner:
 
 	; see if not starting on boundary
 	ldx	VGI_RX1
@@ -164,9 +199,12 @@ simple_rectangle_loop:
 	adc	XRUN
 	sta	XRUN
 
-no_shift:
+	lda	HGR_BITS
+	jsr	COLOR_SHIFT
 
 
+;no_shift:
+
 	; draw common
 draw_run:
 	lda	XRUN