diff --git a/eeschema/sim/ngspice.cpp b/eeschema/sim/ngspice.cpp
index 3ba4b97662..d9990457c6 100644
--- a/eeschema/sim/ngspice.cpp
+++ b/eeschema/sim/ngspice.cpp
@@ -207,7 +207,7 @@ bool NGSPICE::LoadNetlist( const string& aNetlist )
         m_netlist += std::string( line ) + std::string( "\n" );
     }
 
-    lines.push_back( nullptr );
+    lines.push_back( nullptr ); // sentinel, as requested in ngSpice_Circ description
     m_ngSpice_Circ( lines.data() );
 
     for( auto line : lines )
diff --git a/eeschema/sim/sim_plot_frame.cpp b/eeschema/sim/sim_plot_frame.cpp
index fbf344da46..850e586c12 100644
--- a/eeschema/sim/sim_plot_frame.cpp
+++ b/eeschema/sim/sim_plot_frame.cpp
@@ -87,6 +87,10 @@ public:
             case SIM_RUNNING:
                 event = new wxCommandEvent( EVT_SIM_STARTED );
                 break;
+
+            default:
+                wxFAIL;
+                return;
         }
 
         wxQueueEvent( m_parent, event );