diff --git a/th04/formats/cdg.h b/th04/formats/cdg.h
new file mode 100644
index 00000000..fd508d10
--- /dev/null
+++ b/th04/formats/cdg.h
@@ -0,0 +1,5 @@
+// ORs a single plane of the CDG image in the given [slot] into the given
+// VRAM destination plane at (⌊x/8⌋*8, y), wrapped vertically.
+void pascal cdg_put_plane_roll(
+	int x, int y, int slot, vram_plane_t plane_src, void __seg *plane_dst
+);
diff --git a/th04/formats/cdg_put_plane_roll.asm b/th04/formats/cdg_put_plane_roll.asm
new file mode 100644
index 00000000..2d2686cf
--- /dev/null
+++ b/th04/formats/cdg_put_plane_roll.asm
@@ -0,0 +1,80 @@
+public CDG_PUT_PLANE_ROLL
+cdg_put_plane_roll	proc far
+
+@@plane_dst	= word ptr [bp+6]
+@@plane_src	= word ptr [bp+8]
+@@slot     	= word ptr [bp+10]
+@@y        	= word ptr [bp+12]
+@@x        	= word ptr [bp+14]
+
+@@stride_backwards equ dx
+@@h equ bx
+
+	push	bp
+	mov	bp, sp
+	push	si
+	push	di
+	mov	ax, @@plane_dst
+	mov	es, ax
+	mov	si, @@slot
+	shl	si, 4
+	add	si, offset _cdg_slots
+	mov	di, @@x
+	sar	di, 3
+	mov	@@h, [si+CDGSlot.pixel_height]
+	mov	ax, @@y
+	add	ax, @@h
+	dec	ax
+	shl	ax, 6
+	add	di, ax
+	shr	ax, 2
+	add	di, ax
+	mov	ax, [si+CDGSlot.width_divided_by_32]
+	mov	word ptr cs:@@width_dwords, ax
+	jmp	short $+2
+	shl	ax, 2
+	add	ax, ROW_SIZE
+	mov	@@stride_backwards, ax
+	push	ds
+	mov	ax, [si+CDGSlot.sgm_colors]
+	mov	si, [si+CDGSlot.bitplane_size]
+	mov	ds, ax
+	mov	cx, @@plane_src
+	inc	cx
+	mov	ax, si
+	neg	si
+
+@@plane_src_num_to_offset:
+	add	si, ax
+	loop	@@plane_src_num_to_offset
+	cmp	di, (ROW_SIZE * RES_Y)
+	jb	short @@start_blitting
+	sub	di, (ROW_SIZE * RES_Y)
+
+@@start_blitting:
+	cld
+	nop
+
+@@next_row:
+@@width_dwords equ $+1
+	mov	cx, 1234h
+
+@@blit_dword:
+	mov	eax, [si]
+	or	es:[di], eax
+	add	si, 4
+	add	di, 4
+	loop	@@blit_dword
+	sub	di, @@stride_backwards
+	jge	short @@more_rows?
+	add	di, (ROW_SIZE * RES_Y)
+
+@@more_rows?:
+	dec	@@h
+	jnz	short @@next_row
+	pop	ds
+	pop	di
+	pop	si
+	pop	bp
+	retf	0Ah
+cdg_put_plane_roll	endp
diff --git a/th04_main.asm b/th04_main.asm
index 0deb9ace..2eb130d7 100644
--- a/th04_main.asm
+++ b/th04_main.asm
@@ -7245,7 +7245,7 @@ loc_EC24:
 		push	[bp+var_2]
 		push	110000h
 		push	0E000h
-		call	far ptr	loc_1371A
+		call	cdg_put_plane_roll
 		inc	si
 
 loc_EC51:
@@ -15149,74 +15149,7 @@ include th02/initmain.asm
 		db    0
 
 include th04/formats/cdg_put_noalpha.asm
-loc_1371A:
-		push	bp
-		mov	bp, sp
-		push	si
-		push	di
-		mov	ax, [bp+6]
-		mov	es, ax
-		mov	si, [bp+0Ah]
-		shl	si, 4
-		add	si, offset _cdg_slots
-		mov	di, [bp+0Eh]
-		sar	di, 3
-		mov	bx, [si+4]
-		mov	ax, [bp+0Ch]
-		add	ax, bx
-		dec	ax
-		shl	ax, 6
-		add	di, ax
-		shr	ax, 2
-		add	di, ax
-		mov	ax, [si+8]
-		mov	word ptr cs:loc_13778+1, ax
-		jmp	short $+2
-		shl	ax, 2
-		add	ax, 50h	; 'P'
-		mov	dx, ax
-		push	ds
-		mov	ax, [si+0Eh]
-		mov	si, [si]
-		mov	ds, ax
-		mov	cx, [bp+8]
-		inc	cx
-		mov	ax, si
-		neg	si
-
-loc_13768:
-		add	si, ax
-		loop	loc_13768
-		cmp	di, 7D00h
-		jb	short loc_13776
-		sub	di, 7D00h
-
-loc_13776:
-		cld
-		nop
-
-loc_13778:
-		mov	cx, 1234h
-
-loc_1377B:
-		mov	eax, [si]
-		or	es:[di], eax
-		add	si, 4
-		add	di, 4
-		loop	loc_1377B
-		sub	di, dx
-		jge	short loc_13792
-		add	di, 7D00h
-
-loc_13792:
-		dec	bx
-		jnz	short loc_13778
-		pop	ds
-		pop	di
-		pop	si
-		pop	bp
-		retf	0Ah
-
+include th04/formats/cdg_put_plane_roll.asm
 include th04/hardware/input_sense.asm
 include th04/snd/se.asm
 include th04/formats/cdg_load.asm