diff --git a/Userland/Applications/PixelPaint/BrushTool.cpp b/Userland/Applications/PixelPaint/BrushTool.cpp
index 774a819781..dea6e3da4a 100644
--- a/Userland/Applications/PixelPaint/BrushTool.cpp
+++ b/Userland/Applications/PixelPaint/BrushTool.cpp
@@ -39,7 +39,10 @@ void BrushTool::on_mousemove(Layer& layer, GUI::MouseEvent& event, GUI::MouseEve
         return;
 
     draw_line(layer.bitmap(), m_editor->color_for(event), m_last_position, event.position());
-    layer.did_modify_bitmap();
+
+    auto modified_rect = Gfx::IntRect::from_two_points(m_last_position, event.position()).inflated(m_size * 2, m_size * 2);
+
+    layer.did_modify_bitmap(modified_rect);
     m_last_position = event.position();
     m_was_drawing = true;
 }