diff --git a/theta/include/theta_set_difference_base_impl.hpp b/theta/include/theta_set_difference_base_impl.hpp
index 14708f9..4ab98a8 100644
--- a/theta/include/theta_set_difference_base_impl.hpp
+++ b/theta/include/theta_set_difference_base_impl.hpp
@@ -17,6 +17,9 @@
  * under the License.
  */
 
+#ifndef THETA_A_SET_DIFFERENCE_BASE_IMPL_HPP_
+#define THETA_A_SET_DIFFERENCE_BASE_IMPL_HPP_
+
 #include <algorithm>
 
 #include "conditional_back_inserter.hpp"
@@ -78,3 +81,5 @@
 }
 
 } /* namespace datasketches */
+
+#endif
diff --git a/theta/include/theta_sketch_impl.hpp b/theta/include/theta_sketch_impl.hpp
index 0bee4c9..1335e59 100644
--- a/theta/include/theta_sketch_impl.hpp
+++ b/theta/include/theta_sketch_impl.hpp
@@ -220,6 +220,7 @@
 auto update_theta_sketch_alloc<A>::end() const -> const_iterator {
   return const_iterator(nullptr, 0, 1 << table_.lg_cur_size_);
 }
+
 template<typename A>
 compact_theta_sketch_alloc<A> update_theta_sketch_alloc<A>::compact(bool ordered) const {
   return compact_theta_sketch_alloc<A>(*this, ordered);