diff --git a/src/utils/optional_bool.hpp b/src/utils/optional_bool.hpp
index 3d00d23..ebd063d 100644
--- a/src/utils/optional_bool.hpp
+++ b/src/utils/optional_bool.hpp
@@ -1,5 +1,6 @@
 #pragma once
 
+#include <ostream>
 #include <string>
 
 struct OptionalBool