diff --git a/model/sync-digest.h b/model/sync-digest.h
index 15c7278..42cfd81 100644
--- a/model/sync-digest.h
+++ b/model/sync-digest.h
@@ -108,6 +108,14 @@
   inline Digest &
   operator << (uint32_t value);
 
+  /**
+   * @brief Checks if the stored hash is zero-root hash
+   *
+   * Zero-root hash is a valid hash that optimally represents an empty state
+   */
+  bool
+  zero () const;
+  
 private:
   Digest &
   operator = (Digest &digest) { return *this; }