diff --git a/examples/embedded_linux/src/main.rs b/examples/embedded_linux/src/main.rs
index ebc7171..172630a 100644
--- a/examples/embedded_linux/src/main.rs
+++ b/examples/embedded_linux/src/main.rs
@@ -13,6 +13,8 @@ use lin_hal::sysfs_gpio::Direction;
 use lin_hal::Delay;
 
 // activate spi, gpio in raspi-config
+// needs to be run with sudo because of some sysfs_gpio permission problems and follow-up timing problems
+// see https://github.com/rust-embedded/rust-sysfs-gpio/issues/5 and follow-up issues
 
 
 // DigitalIn Hack as long as it's not in the linux_embedded_hal
diff --git a/src/drawing/mod.rs b/src/drawing/mod.rs
index 6c7741f..85f7b2e 100644
--- a/src/drawing/mod.rs
+++ b/src/drawing/mod.rs
@@ -87,7 +87,7 @@ impl Graphics {
     pub fn draw_pixel(&self, buffer: &mut[u8], x: u16, y: u16, color: &Color) {
         let (idx, bit) = match self.rotation {
             Displayorientation::Rotate0 | Displayorientation::Rotate180 
-                => ((x + self.width * y) / 8,
+                => ((x / 8 + (self.width / 8) * y) ,
                     0x80 >> (x % 8)),
             Displayorientation::Rotate90 | Displayorientation::Rotate270
                 => (y / 8 * self.width + x,