diff --git a/src/core/thread/network_data.hpp b/src/core/thread/network_data.hpp
index b5d2d3605..37ae414e1 100644
--- a/src/core/thread/network_data.hpp
+++ b/src/core/thread/network_data.hpp
@@ -92,7 +92,7 @@ class NetworkData : public InstanceLocator
 public:
     enum
     {
-        kMaxSize = 255, ///< Maximum size of Thread Network Data in bytes.
+        kMaxSize = 254, ///< Maximum size of Thread Network Data in bytes.
     };
 
     /**