diff --git a/lib/config.cc b/lib/config.cc
index b4270ee4..86880c4d 100644
--- a/lib/config.cc
+++ b/lib/config.cc
@@ -442,7 +442,7 @@ void Config::clearOptions()
     invalidate();
 }
 
-static void setFluxSourceImpl(std::string filename, FluxSourceProto* proto)
+static void setFluxSourceImpl(const std::string& filename, FluxSourceProto* proto)
 {
     for (const auto& it : fluxConstructors)
     {
@@ -464,7 +464,7 @@ void Config::setFluxSource(std::string filename)
     setFluxSourceImpl(filename, overrides()->mutable_flux_source());
 }
 
-static void setFluxSinkImpl(std::string filename, FluxSinkProto* proto)
+static void setFluxSinkImpl(const std::string& filename, FluxSinkProto* proto)
 {
     for (const auto& it : fluxConstructors)
     {
diff --git a/src/gui/idlepanel.cc b/src/gui/idlepanel.cc
index 69194c0d..31748b89 100644
--- a/src/gui/idlepanel.cc
+++ b/src/gui/idlepanel.cc
@@ -224,8 +224,23 @@ public:
 
             case SELECTEDSOURCE_FLUX:
             {
-                globalConfig().setFluxSink(_selectedFluxfilename);
-                globalConfig().setFluxSource(_selectedFluxfilename);
+                try
+                {
+                    globalConfig().setFluxSink(_selectedFluxfilename);
+                }
+                catch (const InapplicableValueException* e)
+                {
+                    /* ignore */
+                }
+
+                try
+                {
+                    globalConfig().setFluxSource(_selectedFluxfilename);
+                }
+                catch (const InapplicableValueException* e)
+                {
+                    /* ignore */
+                }
                 break;
             }
 
@@ -587,12 +602,12 @@ private:
             /* The current set of options is invalid for some reason. Just
              * swallow the errors. */
         }
-	catch (const ErrorException& e)
-	{
-	    /* This really isn't supposed to happen, but sometimes does and
-	     * it crashes the whole program. */
-	    return;
-	}
+        catch (const ErrorException& e)
+        {
+            /* This really isn't supposed to happen, but sometimes does and
+             * it crashes the whole program. */
+            return;
+        }
 
         assert(!wxGetApp().IsWorkerThreadRunning());
 
diff --git a/src/gui/main.cc b/src/gui/main.cc
index 44a40455..f4817631 100644
--- a/src/gui/main.cc
+++ b/src/gui/main.cc
@@ -53,11 +53,19 @@ private:
 
 bool FluxEngineApp::OnInit()
 {
+	try
+	{
     wxImage::AddHandler(new wxPNGHandler());
     Bind(EXEC_EVENT_TYPE, &FluxEngineApp::OnExec, this);
     _mainWindow = CreateMainWindow();
     _mainWindow->Show(true);
     return true;
+	}
+	catch (const ErrorException* e)
+	{
+		fmt::print(stderr, "Exception on startup: {}\n", e->message);
+		exit(1);
+	}
 }
 
 wxThread::ExitCode FluxEngineApp::Entry()