diff --git a/src/hydro/Gadget2/hydro_part.h b/src/hydro/Gadget2/hydro_part.h
index 98ad9c86be620454a92a5bb01e1127385b561642..4cdbcb7127d0ec74658fa52dad5f5abd6d9a6a1a 100644
--- a/src/hydro/Gadget2/hydro_part.h
+++ b/src/hydro/Gadget2/hydro_part.h
@@ -32,6 +32,7 @@
  */
 
 #include "chemistry_struct.h"
+#include "cooling_struct.h"
 
 /* Extra particle data not needed during the SPH loops over neighbours. */
 struct xpart {