diff --git a/include/maxwell/maxwell_interface.h b/include/maxwell/maxwell_interface.h
index 98e0852c996711e749468d673e5ef4519eed429d..af0379ec1113d414241eae07122ac44c3c8ab7f2 100644
--- a/include/maxwell/maxwell_interface.h
+++ b/include/maxwell/maxwell_interface.h
@@ -303,7 +303,7 @@ struct solver_state_gpu
     double                              curr_time;
     size_t                              curr_timestep;
 
-#ifndef /* TM_NEW_CURLS */
+#ifndef TM_NEW_CURLS
     field_gpu                           dx;
     field_gpu                           dy;
     field_gpu                           dz;