diff --git a/eeschema/sim/sim_panel_base.cpp b/eeschema/sim/sim_panel_base.cpp
index 22c129ad9e..9e51e8f776 100644
--- a/eeschema/sim/sim_panel_base.cpp
+++ b/eeschema/sim/sim_panel_base.cpp
@@ -74,15 +74,6 @@ 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 4e04596542..494d3b1fa3 100644
--- a/eeschema/sim/sim_panel_base.h
+++ b/eeschema/sim/sim_panel_base.h
@@ -27,6 +27,7 @@
 #define __SIM_PLOT_PANEL_BASE_H
 
 #include "sim_types.h"
+#include "netlist_exporter_pspice_sim.h"
 #include <wx/panel.h>
 #include <wx/sizer.h>
 #include <wx/stattext.h>
@@ -34,6 +35,8 @@
 
 class SIM_PANEL_BASE : public wxWindow
 {
+    friend class SIM_WORKBOOK;
+
 public:
     SIM_PANEL_BASE();
     SIM_PANEL_BASE( wxString aCommand );
@@ -46,10 +49,21 @@ public:
 
     SIM_TYPE GetType() const;
 
-    void SetSimCommand( const wxString& aSimCommand );
+protected:
+    // Some members should be accessible from outside only through a workbook object, to prevent
+    // anyone from modifying the state without its knowledge. Otherwise we risk some things not
+    // getting saved.
 
     const wxString& GetSimCommand() const { return m_simCommand; }
 
+    void 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;
+    }
+
 private:
     wxString m_simCommand;
 };
diff --git a/eeschema/sim/sim_plot_frame.cpp b/eeschema/sim/sim_plot_frame.cpp
index b62bb3faab..f6442dbd79 100644
--- a/eeschema/sim/sim_plot_frame.cpp
+++ b/eeschema/sim/sim_plot_frame.cpp
@@ -472,7 +472,7 @@ void SIM_PLOT_FRAME::StartSimulation( const wxString& aSimCommand )
         SIM_PANEL_BASE* plotPanel = currentPlotWindow();
 
         if( plotPanel && m_workbook->HasPlotPanel( plotPanel ) )
-            m_exporter->SetSimCommand( plotPanel->GetSimCommand() );
+            m_exporter->SetSimCommand( m_workbook->GetSimCommand( plotPanel ) );
     }
     else
     {
@@ -1041,7 +1041,7 @@ bool SIM_PLOT_FRAME::saveWorkbook( const wxString& aPath )
     for( const SIM_PANEL_BASE*& plotPanel : plotPanels )
     {
         file.AddLine( wxString::Format( "%d", plotPanel->GetType() ) );
-        file.AddLine( plotPanel->GetSimCommand() );
+        file.AddLine( m_workbook->GetSimCommand( plotPanel ) );
 
         const SIM_PLOT_PANEL* panel = dynamic_cast<const SIM_PLOT_PANEL*>( plotPanel );
 
@@ -1401,14 +1401,14 @@ void SIM_PLOT_FRAME::onSettings( wxCommandEvent& event )
     }
 
     if( m_workbook->HasPlotPanel( plotPanelWindow ) )
-        m_settingsDlg->SetSimCommand( plotPanelWindow->GetSimCommand() );
+        m_settingsDlg->SetSimCommand( m_workbook->GetSimCommand( plotPanelWindow ) );
 
     if( m_settingsDlg->ShowModal() == wxID_OK )
     {
         wxString oldCommand;
 
         if( m_workbook->HasPlotPanel( plotPanelWindow ) )
-            oldCommand = plotPanelWindow->GetSimCommand();
+            oldCommand = m_workbook->GetSimCommand( plotPanelWindow );
         else
             oldCommand = wxString();
 
@@ -1428,7 +1428,7 @@ void SIM_PLOT_FRAME::onSettings( wxCommandEvent& event )
         else
         {
             // Update simulation command in the current plot
-            plotPanelWindow->SetSimCommand( newCommand );
+            m_workbook->SetSimCommand( plotPanelWindow, newCommand );
         }
 
         m_simulator->Init();
diff --git a/eeschema/sim/sim_workbook.h b/eeschema/sim/sim_workbook.h
index fc971ef209..e48984f4a9 100644
--- a/eeschema/sim/sim_workbook.h
+++ b/eeschema/sim/sim_workbook.h
@@ -62,6 +62,16 @@ public:
         m_plots.at( aPlotPanel ).pos = pos;
     }
 
+    void SetSimCommand( SIM_PANEL_BASE* aPlotPanel, const wxString& aSimCommand )
+    {
+        aPlotPanel->SetSimCommand( aSimCommand );
+    }
+
+    const wxString& GetSimCommand( const SIM_PANEL_BASE* aPlotPanel )
+    {
+        return aPlotPanel->GetSimCommand();
+    }
+
     void ClrModified() { m_flagModified = false; }
     bool IsModified() const { return m_flagModified; }