diff --git a/bmp2h.py b/bmp2h.py
index cd3a517..e93db03 100644
--- a/bmp2h.py
+++ b/bmp2h.py
@@ -13,24 +13,23 @@ def get_bytestring(fname):
 const uint8_t """ + bmp_name + """_data[] PROGMEM = {""", end="")
 
     with Image.open(fname) as im:
-        w = im.size[0]
-        h = im.size[1]
+        w, h = im.size
         im = im.convert('L')
         pix = im.load()
 
-        for i in range(w*h // 8):
-            x = (i * 8) % w
-            y = i // (w // 8)
-            b = 0
-            if x == 0:
-                print("")
-            for bit in range(8):
-                if x + bit >= w: break
-                if y >= h: break
-                if pix[x + bit, y] < 127:
-                    b += 1 << bit
-            print("\t", hex(b), end=", ")
+        row_bytes = (w + 7) // 8
 
+        for y in range(h):
+            print("")
+            for bx in range(row_bytes):
+                x = bx * 8
+                b = 0
+                for bit in range(8):
+                    if x + bit >= w:
+                        break
+                    if pix[x + bit, y] < 127:
+                        b += 1 << bit
+                print("\t", hex(b), end=", ")
 
 
     print("""
diff --git a/esp-gfx/gfx.c b/esp-gfx/gfx.c
index 3f3e1ff..174f78c 100644
--- a/esp-gfx/gfx.c
+++ b/esp-gfx/gfx.c
@@ -93,11 +93,17 @@ void gfx_fill_box(const gfx_canvas_t *canvas, const uint8_t pos_x, const uint8_t
 
 void gfx_draw_bitmap(const gfx_canvas_t *canvas, const uint8_t pos_x, const uint8_t pos_y, const gfx_bitmap_t bmp, const bool inverted) {
 	void (*draw_cb)(void* ctx, uint8_t x, uint8_t y) = inverted ? canvas->clear_pixel_callback : canvas->draw_pixel_callback;
-	for (uint16_t i = 0; i < (uint16_t)(bmp.height * bmp.width / 8); i++) {
-		const uint8_t x = (i * 8) % bmp.width;
-		const uint8_t y = i / (bmp.width / 8);
-		for (uint8_t j = 0; j < 8; j++)
-			if (bmp.data[i] & (1 << j))
-				draw_cb(canvas->ctx, pos_x + x + j, pos_y + y);
+	const uint8_t row_bytes = (bmp.width + 7) / 8;
+
+	for (uint8_t y = 0; y < bmp.height; y++) {
+		for (uint8_t bx = 0; bx < row_bytes; bx++) {
+			const uint8_t byte = bmp.data[y * row_bytes + bx];
+			const uint8_t x = bx * 8;
+			for (uint8_t j = 0; j < 8; j++) {
+				if (x + j >= bmp.width) break;
+				if (byte & (1 << j))
+					draw_cb(canvas->ctx, pos_x + x + j, pos_y + y);
+			}
+		}
 	}
 }
\ No newline at end of file