diff --git a/Source/Evolve/WarpXEvolve.cpp b/Source/Evolve/WarpXEvolve.cpp
index 5ff7a4cba..698ec4573 100644
--- a/Source/Evolve/WarpXEvolve.cpp
+++ b/Source/Evolve/WarpXEvolve.cpp
@@ -506,8 +506,8 @@ WarpX::OneStep_nosub (Real cur_time)
             FillBoundaryH(guard_cells.ng_FieldSolver);
             FillBoundaryM(guard_cells.ng_FieldSolver);
             // ApplyExternalFieldExcitation
-            ApplyExternalFieldExcitationOnGrid(ExternalFieldType::HfieldExternal); // apply H external excitation; soft source to be fixed
-            ApplyExternalFieldExcitationOnGrid(ExternalFieldType::HbiasfieldExternal); // apply H external excitation; soft source to be fixed
+            ApplyExternalFieldExcitationOnGrid(ExternalFieldType::HfieldExternal, DtType::FirstHalf); // apply H external excitation; soft source to be fixed
+            ApplyExternalFieldExcitationOnGrid(ExternalFieldType::HbiasfieldExternal, DtType::FirstHalf); // apply H external excitation; soft source to be fixed
 
         } else {
             amrex::Abort("unsupported em_solver_medium for M field");