diff --git a/imagescrollareagl.cpp b/imagescrollareagl.cpp
index 9def140..8d11a5d 100644
--- a/imagescrollareagl.cpp
+++ b/imagescrollareagl.cpp
@@ -366,7 +366,9 @@ void ImageWidget::paintGL()
         QPainter painter(this);
         const int w = width()/THUMB_SIZE_BORDER;
         const int off = (THUMB_SIZE_BORDER - THUMB_SIZE) / 2;
-        for(int i=0; i < m_thumbnailCount; i++)
+        int start = std::max((int)(m_dy / THUMB_SIZE_BORDER_Y * w - w), 0);
+        int end = std::min((int)(m_dy + m_height) / THUMB_SIZE_BORDER_Y * w + w, m_thumbnailCount);
+        for(int i=start; i < end; i++)
         {
             float x = (i % w) * THUMB_SIZE_BORDER;
             float y = i / w * THUMB_SIZE_BORDER_Y + THUMB_SIZE - m_dy + off;