3 files changed, 19 insertions, 7 deletions
diff --git a/Source/Diagnostics/WarpXIO.cpp b/Source/Diagnostics/WarpXIO.cpp
index 416969d7e..58fdccf22 100644
--- a/Source/Diagnostics/WarpXIO.cpp
+++ b/Source/Diagnostics/WarpXIO.cpp
@@ -540,14 +540,14 @@ WarpX::WriteOpenPMDFile () const
 #ifdef WARPX_USE_OPENPMD
     const auto step = istep[0];
 
+    m_OpenPMDPlotWriter->SetStep(step);
+
     Vector<std::string> varnames; // Name of the written fields
     Vector<MultiFab> mf_avg; // contains the averaged, cell-centered fields
     Vector<const MultiFab*> output_mf; // will point to the data to be written
     Vector<Geometry> output_geom;
 
     prepareFields(step, varnames, mf_avg, output_mf, output_geom);
-
-    m_OpenPMDPlotWriter->SetStep(step);
     // fields: only dumped for coarse level
     m_OpenPMDPlotWriter->WriteOpenPMDFields(
         varnames, *output_mf[0], output_geom[0], step, t_new[0]);
diff --git a/Source/Diagnostics/WarpXOpenPMD.H b/Source/Diagnostics/WarpXOpenPMD.H
index bd18ec8c1..9ffcd0f37 100644
--- a/Source/Diagnostics/WarpXOpenPMD.H
+++ b/Source/Diagnostics/WarpXOpenPMD.H
@@ -88,6 +88,11 @@ public:
 
   ~WarpXOpenPMDPlot();
 
+  /** Set Iteration Step for the series
+   *
+   * @note If an iteration has been written, then it will give a warning
+   *
+   */
   void SetStep(int ts);
 
   void WriteOpenPMDParticles(const std::unique_ptr<MultiParticleContainer>&);
diff --git a/Source/Diagnostics/WarpXOpenPMD.cpp b/Source/Diagnostics/WarpXOpenPMD.cpp
index 6f76906e3..cacf6367d 100644
--- a/Source/Diagnostics/WarpXOpenPMD.cpp
+++ b/Source/Diagnostics/WarpXOpenPMD.cpp
@@ -16,7 +16,7 @@
 #include <sstream>
 #include <tuple>
 #include <utility>
-
+#include <iostream>
 
 namespace detail
 {
@@ -140,12 +140,19 @@ void WarpXOpenPMDPlot::GetFileName(std::string& filename)
 
 void WarpXOpenPMDPlot::SetStep(int ts)
 {
-  if (ts < 0)
-    return;
+  AMREX_ALWAYS_ASSERT_WITH_MESSAGE(ts >= 0 , "openPMD iterations are unsigned");
+
+  if (m_CurrentStep >= ts) {
+      // note m_Series is reset in Init(), so using m_Series->iterations.contains(ts) is only able to check the
+      // last written step in m_Series's life time, but not other earlier written steps by other m_Series
+      std::string warnMsg = " Warning from openPMD writer: Already written iteration:"+std::to_string(ts);
+      std::cout<<warnMsg<<std::endl;
+      amrex::Warning(warnMsg);
+  }
 
-  m_CurrentStep =  ts;
+    m_CurrentStep =  ts;
+    Init(openPMD::AccessType::CREATE);
 
-  Init(openPMD::AccessType::CREATE);
 }
 
 void