diff --git a/einkfb.c b/einkfb.c
index b5a3bf50b..b87c4905f 100644
--- a/einkfb.c
+++ b/einkfb.c
@@ -41,8 +41,8 @@ inline void fbInvert4BppTo8Bpp(FBInfo *fb) {
 	fb_pitch = fb->real_buf->pitch;
 
 	/* copy bitmap from 4bpp shadow blitbuffer to framebuffer */
-	for (i = (h-1); i > 0; i--) {
-		for (j = (w-1)/2; j > 0; j--) {
+	for (i = (h-1); i >= 0; i--) {
+		for (j = (w-1)/2; j >= 0; j--) {
 			fb_buf[i*fb_pitch + j*2] = shadow_buf[i*pitch + j];
 			fb_buf[i*fb_pitch + j*2] &= 0xF0;
 			fb_buf[i*fb_pitch + j*2] |= shadow_buf[i*pitch + j]>>4 & 0x0F;
@@ -60,18 +60,18 @@ inline void fb4BppTo8Bpp(FBInfo *fb) {
 
 	shadow_buf = fb->buf->data;
 	fb_buf = fb->real_buf->data;
-	/* h is 1024 for PaperWhite */
+	/* h is 1024 for PaperWhite's shadow buffer */
 	h = fb->buf->h;
-	/* w is 758 for PaperWhite */
+	/* w is 758 for PaperWhite's shadow buffer */
 	w = fb->buf->w;
-	/* pitch is 384 for shadow buffer */
+	/* pitch is 376 for shadow buffer */
 	pitch = fb->buf->pitch;
-	/* pitch is 768 for PaperWhite */
+	/* pitch is 768 for PaperWhite's framebuffer */
 	fb_pitch = fb->real_buf->pitch;
 
 	/* copy bitmap from 4bpp shadow blitbuffer to framebuffer */
-	for (i = (h-1); i > 0; i--) {
-		for (j = (w-1)/2; j > 0; j--) {
+	for (i = (h-1); i >= 0; i--) {
+		for (j = (w-1)/2; j >= 0; j--) {
 			fb_buf[i*fb_pitch + j*2] = shadow_buf[i*pitch + j];
 			fb_buf[i*fb_pitch + j*2] &= 0xF0;
 			fb_buf[i*fb_pitch + j*2] |= shadow_buf[i*pitch + j]>>4 & 0x0F;
@@ -222,10 +222,16 @@ static int openFrameBuffer(lua_State *L) {
 	}
 	
 	if (fb->vinfo.bits_per_pixel == 8) {
-		/* for 8bpp K4, PaperWhite, we create a shadow 4bpp blitbuffer. These
-		 * models use 16 scale 8bpp framebuffer, so we still cheat it as 4bpp
+		/* for 8bpp K4, PaperWhite, we create a shadow 4bpp blitbuffer.
+		 * These models use 16 scale 8bpp framebuffer, so they are
+		 * actually fake 8bpp FB. Therefore, we still treat them as 4bpp
+		 *
+		 * For PaperWhite, the screen width is 758, but FB's line_length
+		 * is 768. So when doing the screen update, you still need to
+		 * fill 768 pixels per line, but the trailing 10 px for each
+		 * line is actually ignored by driver.
 		 * */
-		fb->buf->pitch = fb->finfo.line_length / 2;
+		fb->buf->pitch = fb->vinfo.xres / 2;
 
 		fb->buf->data = (uint8_t *)calloc(fb->buf->pitch * fb->vinfo.yres, sizeof(uint8_t));
 		if (!fb->buf->data) {
diff --git a/frontend/ui/screen.lua b/frontend/ui/screen.lua
index 5844af55d..2f5a8840a 100644
--- a/frontend/ui/screen.lua
+++ b/frontend/ui/screen.lua
@@ -42,7 +42,6 @@ Codes for rotation modes:
 Screen = {
 	width = 0,
 	height = 0,
-	pitch = 0,
 	native_rotation_mode = nil,
 	cur_rotation_mode = 0,
 
@@ -53,12 +52,11 @@ Screen = {
 }
 
 function Screen:init()
-	_, self.height = self.fb:getSize()
-	-- for unknown strange reason, pitch*2 is less than screen width in KPW
-	-- so we need to calculate width by pitch here
-	self.pitch = self.fb:getPitch()
-	self.width = self.pitch * 2
-	self.bb = Blitbuffer.new(self.width, self.height, self.pitch)
+	-- for unknown strange reason, pitch*2 is 10 px more than screen width in KPW
+	self.width, self.height = self.fb:getSize()
+	-- Blitbuffer still uses inverted 4bpp bitmap, so pitch should be
+	-- (self.width / 2)
+	self.bb = Blitbuffer.new(self.width, self.height, self.width/2)
 	if self.width > self.height then
 		-- For another unknown strange reason, self.fb:getOrientation always
 		-- return 0 in KPW, even though we are in landscape mode.
@@ -102,7 +100,7 @@ function Screen:getDPI()
 end
 
 function Screen:getPitch()
-	return self.ptich
+	return self.fb:getPitch()
 end
 
 function Screen:getNativeRotationMode()
@@ -133,8 +131,7 @@ function Screen:setRotationMode(mode)
 	end
 	self.cur_rotation_mode = mode
 	self.bb:free()
-	self.pitch = self.width/2
-	self.bb = Blitbuffer.new(self.width, self.height, self.pitch)
+	self.bb = Blitbuffer.new(self.width, self.height, self.width/2)
 	-- update mode for input module
 	Input.rotation = mode
 end
@@ -170,11 +167,11 @@ function Screen:saveCurrentBB()
 	local width, height = self:getWidth(), self:getHeight()
 
 	if not self.saved_bb then
-		self.saved_bb = Blitbuffer.new(width, height, self:getPitch())
+		self.saved_bb = Blitbuffer.new(width, height, self.width/2)
 	end
 	if self.saved_bb:getWidth() ~= width then
 		self.saved_bb:free()
-		self.saved_bb = Blitbuffer.new(width, height, self:getPitch())
+		self.saved_bb = Blitbuffer.new(width, height, self.width/2)
 	end
 	self.saved_bb:blitFullFrom(self.bb)
 end