diff --git a/src/hydro/Gadget2/hydro_iact.h b/src/hydro/Gadget2/hydro_iact.h
index ad0c279c823dd412b595fa2347e3e3c2e90c1e14..8a4edfe62f59a3fae551fdb65f46987509f89251 100644
--- a/src/hydro/Gadget2/hydro_iact.h
+++ b/src/hydro/Gadget2/hydro_iact.h
@@ -20,6 +20,8 @@
 #ifndef SWIFT_GADGET2_HYDRO_IACT_H
 #define SWIFT_GADGET2_HYDRO_IACT_H
 
+#include "minmax.h"
+
 /**
  * @brief SPH interaction functions following the Gadget-2 version of SPH.
  *