diff --git a/theta/include/theta_union.hpp b/theta/include/theta_union.hpp
index 7fa2095..6cf8ccc 100644
--- a/theta/include/theta_union.hpp
+++ b/theta/include/theta_union.hpp
@@ -24,7 +24,7 @@
 #include <functional>
 #include <climits>
 
-#include <theta_sketch.hpp>
+#include "theta_sketch.hpp"
 
 namespace datasketches {