diff --git a/eeschema/sim/sim_panel_base.cpp b/eeschema/sim/sim_panel_base.cpp
index d98b485097..22c129ad9e 100644
--- a/eeschema/sim/sim_panel_base.cpp
+++ b/eeschema/sim/sim_panel_base.cpp
@@ -22,6 +22,7 @@
  * 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA
  */
 
+#include "confirm.h"
 #include "sim_panel_base.h"
 
 #include "sim_plot_frame.h"
@@ -73,6 +74,15 @@ SIM_TYPE SIM_PANEL_BASE::GetType() const
 }
 
 
+void SIM_PANEL_BASE::SetSimCommand( const wxString& aSimCommand )
+{
+    wxCHECK_RET( GetType() == NETLIST_EXPORTER_PSPICE_SIM::CommandToSimType( aSimCommand ),
+                 "Cannot change the type of simulation of the existing plot panel" );
+
+    m_simCommand = aSimCommand;
+}
+
+
 SIM_NOPLOT_PANEL::SIM_NOPLOT_PANEL( wxString aCommand, wxWindow* parent, wxWindowID id,
                                     const wxPoint& pos, const wxSize& size, long style,
                                     const wxString& name ) :
diff --git a/eeschema/sim/sim_panel_base.h b/eeschema/sim/sim_panel_base.h
index 3712b846f0..4e04596542 100644
--- a/eeschema/sim/sim_panel_base.h
+++ b/eeschema/sim/sim_panel_base.h
@@ -46,8 +46,12 @@ public:
 
     SIM_TYPE GetType() const;
 
-protected:
-    const wxString m_simCommand;
+    void SetSimCommand( const wxString& aSimCommand );
+
+    const wxString& GetSimCommand() const { return m_simCommand; }
+
+private:
+    wxString m_simCommand;
 };
 
 
diff --git a/eeschema/sim/sim_plot_frame.cpp b/eeschema/sim/sim_plot_frame.cpp
index 28c696b1d9..16b014a149 100644
--- a/eeschema/sim/sim_plot_frame.cpp
+++ b/eeschema/sim/sim_plot_frame.cpp
@@ -461,7 +461,7 @@ void SIM_PLOT_FRAME::StartSimulation( const wxString& aSimCommand )
         SIM_PANEL_BASE* plotPanel = currentPlotWindow();
 
         if( plotPanel && m_workbook->HasPlotPanel( plotPanel ) )
-            m_exporter->SetSimCommand( m_workbook->GetSimCommand( plotPanel ) );
+            m_exporter->SetSimCommand( plotPanel->GetSimCommand() );
     }
     else
     {
@@ -948,9 +948,8 @@ bool SIM_PLOT_FRAME::loadWorkbook( const wxString& aPath )
         }
 
         wxString        simCommand = file.GetNextLine();
-        SIM_PANEL_BASE* plotPanel = NewPlotPanel( simCommand );
-        m_workbook->SetSimCommand( plotPanel, simCommand );
-        StartSimulation( m_workbook->GetSimCommand( plotPanel ) );
+        NewPlotPanel( simCommand );
+        StartSimulation( simCommand );
 
         // Perform simulation, so plots can be added with values
         do
@@ -1028,12 +1027,11 @@ bool SIM_PLOT_FRAME::saveWorkbook( const wxString& aPath )
 
     for( const SIM_PANEL_BASE*& plotPanel : plotPanels )
     {
-        SIM_WORKBOOK::PLOT_INFO plot = m_workbook->GetPlot( plotPanel );
-
         file.AddLine( wxString::Format( "%d", plotPanel->GetType() ) );
-        file.AddLine( plot.m_simCommand );
+        file.AddLine( plotPanel->GetSimCommand() );
 
         const SIM_PLOT_PANEL* panel = dynamic_cast<const SIM_PLOT_PANEL*>( plotPanel );
+
         if( !panel )
             file.AddLine( wxString::Format( "%llu", 0ull ) );
         else
@@ -1089,16 +1087,8 @@ void SIM_PLOT_FRAME::menuNewPlot( wxCommandEvent& aEvent )
 
     if( SIM_PANEL_BASE::IsPlottable( type ) )
     {
-        SIM_PLOT_PANEL* prevPlot = CurrentPlot();
-        SIM_PLOT_PANEL* newPlot =
-                dynamic_cast<SIM_PLOT_PANEL*>( NewPlotPanel( m_exporter->GetUsedSimCommand() ) );
-
-        // If the previous plot had the same type, copy the simulation command
-        if( prevPlot )
-        {
-            m_workbook->SetSimCommand( newPlot, m_workbook->GetSimCommand( prevPlot ) );
-            updateFrame();
-        }
+        NewPlotPanel( m_exporter->GetUsedSimCommand() );
+        updateFrame();
     }
 }
 
@@ -1404,14 +1394,14 @@ void SIM_PLOT_FRAME::onSettings( wxCommandEvent& event )
     }
 
     if( m_workbook->HasPlotPanel( plotPanelWindow ) )
-        m_settingsDlg->SetSimCommand( m_workbook->GetSimCommand( plotPanelWindow ) );
+        m_settingsDlg->SetSimCommand( plotPanelWindow->GetSimCommand() );
 
     if( m_settingsDlg->ShowModal() == wxID_OK )
     {
         wxString oldCommand;
 
         if( m_workbook->HasPlotPanel( plotPanelWindow ) )
-            oldCommand = m_workbook->GetSimCommand( plotPanelWindow );
+            oldCommand = plotPanelWindow->GetSimCommand();
         else
             oldCommand = wxString();
 
@@ -1428,8 +1418,12 @@ void SIM_PLOT_FRAME::onSettings( wxCommandEvent& event )
         {
             plotPanelWindow = NewPlotPanel( newCommand );
         }
+        else
+        {
+            // Update simulation command in the current plot
+            plotPanelWindow->SetSimCommand( newCommand );
+        }
 
-        m_workbook->SetSimCommand( plotPanelWindow, newCommand );
         m_simulator->Init();
         updateFrame();
     }
diff --git a/eeschema/sim/sim_plot_panel.cpp b/eeschema/sim/sim_plot_panel.cpp
index 0b3df11207..b7e3793807 100644
--- a/eeschema/sim/sim_plot_panel.cpp
+++ b/eeschema/sim/sim_plot_panel.cpp
@@ -386,9 +386,9 @@ void SIM_PLOT_PANEL::prepareDCAxes()
 {
     wxRegEx simCmd( "^.dc[[:space:]]+([[:alnum:]]+\\M).*", wxRE_ADVANCED | wxRE_ICASE );
 
-    if( simCmd.Matches( m_simCommand ) )
+    if( simCmd.Matches( GetSimCommand() ) )
     {
-        switch( static_cast<char>( simCmd.GetMatch( m_simCommand.Lower(), 1 ).GetChar( 0 ) ) )
+        switch( static_cast<char>( simCmd.GetMatch( GetSimCommand().Lower(), 1 ).GetChar( 0 ) ) )
         {
         case 'v':
             m_axis_x =
diff --git a/eeschema/sim/sim_workbook.h b/eeschema/sim/sim_workbook.h
index dc4b2f2d09..fc971ef209 100644
--- a/eeschema/sim/sim_workbook.h
+++ b/eeschema/sim/sim_workbook.h
@@ -33,10 +33,6 @@ public:
 
     struct PLOT_INFO
     {
-        ///< Spice directive used to execute the simulation
-        ///< TODO: use SIM_PANEL_BASE::m_simCommand instead
-        wxString m_simCommand;
-
         ///< The current position of the plot in the notebook
         unsigned int pos;
     };
@@ -66,24 +62,6 @@ public:
         m_plots.at( aPlotPanel ).pos = pos;
     }
 
-    void SetSimCommand( const SIM_PANEL_BASE* aPlotPanel, const wxString& aSimCommand )
-    {
-        if( m_plots.at( aPlotPanel ).m_simCommand != aSimCommand )
-            m_flagModified = true;
-
-        m_plots.at( aPlotPanel ).m_simCommand = aSimCommand;
-    }
-
-    const wxString& GetSimCommand( const SIM_PANEL_BASE* aPlotPanel ) const
-    {
-        return m_plots.at( aPlotPanel ).m_simCommand;
-    }
-
-    PLOT_INFO GetPlot( const SIM_PANEL_BASE* aPlotPanel ) const
-    {
-        return m_plots.at( aPlotPanel );
-    }
-
     void ClrModified() { m_flagModified = false; }
     bool IsModified() const { return m_flagModified; }