diff --git a/gemma/configs.h b/gemma/configs.h
index 447c246..38fab43 100644
--- a/gemma/configs.h
+++ b/gemma/configs.h
@@ -83,6 +83,7 @@ static inline bool EnumValid(LayerAttentionType type) {
 enum class AttentionImpl {
   kOld,
   kFlash,
+  kSentinel,
 };
 
 AttentionImpl GetAttentionImpl(const std::string& impl);
diff --git a/gemma/kv_cache_test.cc b/gemma/kv_cache_test.cc
index bc1f8bc..157b3d9 100644
--- a/gemma/kv_cache_test.cc
+++ b/gemma/kv_cache_test.cc
@@ -1,5 +1,6 @@
 #include "gemma/kv_cache.h"
 
+#include <cstddef>
 #include <vector>
 
 #include "gtest/gtest.h"