diff --git a/ProcessLib/Output/IntegrationPointWriter.h b/ProcessLib/Output/IntegrationPointWriter.h
index 9047e31fe2f7a8cc2c423eb53fa8ab7b11b419df..5bb7302575c22d75ee3391901690d257655551c0 100644
--- a/ProcessLib/Output/IntegrationPointWriter.h
+++ b/ProcessLib/Output/IntegrationPointWriter.h
@@ -8,6 +8,7 @@
  *              http://www.opengeosys.org/project/license
  *
  */
+#include <functional>
 #include <memory>
 #include <nlohmann/json_fwd.hpp>
 #include <vector>