diff --git a/src/window.cc b/src/window.cc
index 1b74f341..78a5fe00 100644
--- a/src/window.cc
+++ b/src/window.cc
@@ -64,6 +64,8 @@ void Window::update_display_buffer()
     m_display_buffer.compute_range();
     m_highlighters(m_display_buffer);
     m_display_buffer.optimize();
+
+    m_timestamp = buffer().timestamp();
 }
 
 void Window::set_position(const DisplayCoord& position)
diff --git a/src/window.hh b/src/window.hh
index 866bb3fb..1433bd2c 100644
--- a/src/window.hh
+++ b/src/window.hh
@@ -46,6 +46,8 @@ public:
     HookManager&         hook_manager()         { return m_hook_manager; }
     const HookManager&   hook_manager()   const { return m_hook_manager; }
 
+    size_t timestamp() const { return m_timestamp; }
+    void   forget_timestamp() { m_timestamp = -1; }
 
 private:
     friend class Buffer;
@@ -66,6 +68,8 @@ private:
 
     HookManager      m_hook_manager;
     OptionManager    m_option_manager;
+
+    size_t m_timestamp = -1;
 };
 
 }