diff --git a/backend/Backend.h b/backend/Backend.h
index a32c57f..821994f 100644
--- a/backend/Backend.h
+++ b/backend/Backend.h
@@ -36,6 +36,8 @@
  protected:
   uint32_t CalcPixOps(const std::map<uint32_t, DrmHwcTwo::HwcLayer *> &z_map,
                       size_t first_z, size_t size);
+  void MarkValidated(std::map<uint32_t, DrmHwcTwo::HwcLayer *> &z_map,
+                     size_t client_first_z, size_t client_size);
   std::tuple<int, int> GetExtraClientRange(
       DrmHwcTwo::HwcDisplay *display,
       const std::vector<DrmHwcTwo::HwcLayer *> &layers, int client_start,