diff --git a/lib/GfxRenderer/GfxRenderer.cpp b/lib/GfxRenderer/GfxRenderer.cpp
index 171bd80..d7afd28 100644
--- a/lib/GfxRenderer/GfxRenderer.cpp
+++ b/lib/GfxRenderer/GfxRenderer.cpp
@@ -132,13 +132,19 @@ void GfxRenderer::displayBuffer(const EInkDisplay::RefreshMode refreshMode) cons
   einkDisplay.displayBuffer(refreshMode);
 }
 
-// TODO: Support partial window update
-// void GfxRenderer::flushArea(const int x, const int y, const int width, const int height) const {
-//   const int rotatedX = y;
-//   const int rotatedY = EInkDisplay::DISPLAY_HEIGHT - 1 - x;
-//
-//   einkDisplay.displayBuffer(EInkDisplay::FAST_REFRESH, rotatedX, rotatedY, height, width);
-// }
+void GfxRenderer::displayWindow(const int x, const int y, const int width, const int height) const {
+  // Rotate coordinates from portrait (480x800) to landscape (800x480)
+  // Rotation: 90 degrees clockwise
+  // Portrait coordinates: (x, y) with dimensions (width, height)
+  // Landscape coordinates: (rotatedX, rotatedY) with dimensions (rotatedWidth, rotatedHeight)
+
+  const int rotatedX = y;
+  const int rotatedY = EInkDisplay::DISPLAY_HEIGHT - 1 - x - width + 1;
+  const int rotatedWidth = height;
+  const int rotatedHeight = width;
+
+  einkDisplay.displayWindow(rotatedX, rotatedY, rotatedWidth, rotatedHeight);
+}
 
 // Note: Internal driver treats screen in command orientation, this library treats in portrait orientation
 int GfxRenderer::getScreenWidth() { return EInkDisplay::DISPLAY_HEIGHT; }
diff --git a/lib/GfxRenderer/GfxRenderer.h b/lib/GfxRenderer/GfxRenderer.h
index e5760a2..cb8b588 100644
--- a/lib/GfxRenderer/GfxRenderer.h
+++ b/lib/GfxRenderer/GfxRenderer.h
@@ -28,6 +28,8 @@ class GfxRenderer {
   static int getScreenWidth();
   static int getScreenHeight();
   void displayBuffer(EInkDisplay::RefreshMode refreshMode = EInkDisplay::FAST_REFRESH) const;
+  // EXPERIMENTAL: Windowed update - display only a rectangular region (portrait coordinates)
+  void displayWindow(int x, int y, int width, int height) const;
   void invertScreen() const;
   void clearScreen(uint8_t color = 0xFF) const;
 
diff --git a/open-x4-sdk b/open-x4-sdk
index fba6220..98a5aa1 160000
--- a/open-x4-sdk
+++ b/open-x4-sdk
@@ -1 +1 @@
-Subproject commit fba62200e2eb49590bb499d9d940bb0fe715d9d9
+Subproject commit 98a5aa1f8969ccd317c9b45bf0fa84b6c82e167f
diff --git a/src/screens/EpubReaderScreen.cpp b/src/screens/EpubReaderScreen.cpp
index fade5da..4e13f3d 100644
--- a/src/screens/EpubReaderScreen.cpp
+++ b/src/screens/EpubReaderScreen.cpp
@@ -31,7 +31,6 @@ void EpubReaderScreen::onEnter() {
 
   epub->setupCacheDir();
 
-  // TODO: Move this to a state object
   if (SD.exists((epub->getCachePath() + "/progress.bin").c_str())) {
     File f = SD.open((epub->getCachePath() + "/progress.bin").c_str());
     uint8_t data[4];
@@ -210,19 +209,20 @@ void EpubReaderScreen::renderScreen() {
       Serial.printf("[%lu] [ERS] Cache not found, building...\n", millis());
 
       {
-        const int textWidth = renderer.getTextWidth(READER_FONT_ID, "Indexing...");
-        constexpr int margin = 20;
-        const int x = (GfxRenderer::getScreenWidth() - textWidth - margin * 2) / 2;
-        constexpr int y = 50;
-        const int w = textWidth + margin * 2;
-        const int h = renderer.getLineHeight(READER_FONT_ID) + margin * 2;
         renderer.grayscaleRevert();
 
-        // TODO: This looks like garbage again, need to implement windowed updates
-        renderer.fillRect(x, y, w, h, 0);
+        const int textWidth = renderer.getTextWidth(READER_FONT_ID, "Indexing...");
+        constexpr int margin = 20;
+        // Round all coordinates to 8 pixel boundaries
+        const int x = ((GfxRenderer::getScreenWidth() - textWidth - margin * 2) / 2 + 7) / 8 * 8;
+        constexpr int y = 56;
+        const int w = (textWidth + margin * 2 + 7) / 8 * 8;
+        const int h = (renderer.getLineHeight(READER_FONT_ID) + margin * 2 + 7) / 8 * 8;
+        renderer.fillRect(x, y, w, h, false);
         renderer.drawText(READER_FONT_ID, x + margin, y + margin, "Indexing...");
         renderer.drawRect(x + 5, y + 5, w - 10, h - 10);
-        renderer.displayBuffer();
+        // EXPERIMENTAL: Still suffers from ghosting
+        renderer.displayWindow(x, y, w, h);
         pagesUntilFullRefresh = 0;
       }