diff --git a/opm/simulators/wells/PerforationData.hpp b/opm/simulators/wells/PerforationData.hpp
index 3a97bf28b..f97c5af6c 100644
--- a/opm/simulators/wells/PerforationData.hpp
+++ b/opm/simulators/wells/PerforationData.hpp
@@ -20,6 +20,8 @@
 #ifndef OPM_PERFORATIONDATA_HEADER_INCLUDED
 #define OPM_PERFORATIONDATA_HEADER_INCLUDED
 
+#include <cstddef>
+
 namespace Opm
 {