diff --git a/opm/simulators/wells/WellContainer.hpp b/opm/simulators/wells/WellContainer.hpp
index 1a517f16e..a27ffa554 100644
--- a/opm/simulators/wells/WellContainer.hpp
+++ b/opm/simulators/wells/WellContainer.hpp
@@ -21,6 +21,7 @@
 #define OPM_WELL_CONTAINER_HEADER_INCLUDED
 
 #include <initializer_list>
+#include <optional>
 #include <stdexcept>
 #include <string>
 #include <unordered_map>