diff --git a/eval/public/containers/container_backed_map_impl.cc b/eval/public/containers/container_backed_map_impl.cc
index 5ac08af92..99d0cdeba 100644
--- a/eval/public/containers/container_backed_map_impl.cc
+++ b/eval/public/containers/container_backed_map_impl.cc
@@ -88,7 +88,7 @@ class CelValueEq {
 absl::optional<CelValue> CelMapBuilder::operator[](CelValue cel_key) const {
   auto item = values_map_.find(cel_key);
   if (item == values_map_.end()) {
-    return absl::nullopt;
+    return std::nullopt;
   }
   return item->second;
 }
diff --git a/eval/public/containers/internal_field_backed_map_impl.cc b/eval/public/containers/internal_field_backed_map_impl.cc
index a879955d1..2d5666c58 100644
--- a/eval/public/containers/internal_field_backed_map_impl.cc
+++ b/eval/public/containers/internal_field_backed_map_impl.cc
@@ -154,7 +154,7 @@ absl::optional<CelValue> FieldBackedMapImpl::operator[](CelValue key) const {
     return CreateErrorValue(arena_, lookup_result.status());
   }
   if (!*lookup_result) {
-    return absl::nullopt;
+    return std::nullopt;
   }
 
   // Get value descriptor treating it as a repeated field.