diff --git a/eeschema/sim/sim_plot_frame.cpp b/eeschema/sim/sim_plot_frame.cpp
index bccf39d6f1..3c5b244364 100644
--- a/eeschema/sim/sim_plot_frame.cpp
+++ b/eeschema/sim/sim_plot_frame.cpp
@@ -476,10 +476,17 @@ void SIM_PLOT_FRAME::StartSimulation( const wxString& aSimCommand )
         return;
     }
 
-    m_simulator->LoadNetlist( formatter.GetString() );
-    updateTuners();
-    applyTuners();
-    m_simulator->Run();
+    std::unique_lock<std::mutex> simulatorLock( m_simulator->GetMutex(), std::try_to_lock );
+
+    if( simulatorLock.owns_lock() )
+    {
+        m_simulator->LoadNetlist( formatter.GetString() );
+        updateTuners();
+        applyTuners();
+        m_simulator->Run();
+    }
+    else
+        DisplayErrorMessage( this, _( "Another simulation is already running." ) );
 }
 
 
@@ -1808,12 +1815,20 @@ void SIM_PLOT_FRAME::onSimUpdate( wxCommandEvent& aEvent )
     }
     else
     {
-        // Incremental update
-        m_simConsole->Clear();
+        std::unique_lock<std::mutex> simulatorLock( m_simulator->GetMutex(), std::try_to_lock );
 
-        // Do not export netlist, it is already stored in the simulator
-        applyTuners();
-        m_simulator->Run();
+        if( simulatorLock.owns_lock() )
+        {
+            // Incremental update
+            m_simConsole->Clear();
+
+            // Do not export netlist, it is already stored in the simulator
+            applyTuners();
+
+            m_simulator->Run();
+        }
+        else
+            DisplayErrorMessage( this, _( "Another simulation is already running." ) );
     }
 }
 
diff --git a/eeschema/sim/spice_simulator.h b/eeschema/sim/spice_simulator.h
index e005da9b1d..d1eb52ffd7 100644
--- a/eeschema/sim/spice_simulator.h
+++ b/eeschema/sim/spice_simulator.h
@@ -30,6 +30,7 @@
 #include "sim_types.h"
 #include "spice_settings.h"
 
+#include <mutex>
 #include <string>
 #include <vector>
 #include <complex>
@@ -63,6 +64,14 @@ public:
      */
     virtual void Init( const SPICE_SIMULATOR_SETTINGS* aSettings = nullptr ) = 0;
 
+    /*
+     * @return mutex for exclusive access to the simulator.
+     */
+    std::mutex& GetMutex()
+    {
+        return m_mutex;
+    }
+
     /**
      * Load a netlist for the simulation.
      *
@@ -204,6 +213,10 @@ protected:
 
     ///< We don't own this.  We are just borrowing it from the #SCHEMATIC_SETTINGS.
     std::shared_ptr<SPICE_SIMULATOR_SETTINGS> m_settings;
+
+private:
+    ///< For interprocess synchronisation.
+    std::mutex m_mutex;
 };
 
 #endif /* SPICE_SIMULATOR_H */