diff --git a/src/gui_builder.cc b/src/gui_builder.cc
index 0e904e6..428891c 100644
--- a/src/gui_builder.cc
+++ b/src/gui_builder.cc
@@ -28,6 +28,11 @@
 #include "gui_builder.hh"
 #include "graphical_preferences_editor.hh"
 
+#include "backend/cpu_policy_exception.hh"
+#include "backend/malformed_policy_exception.hh"
+#include "backend/null_policy_exception.hh"
+#include "backend/user_interrupt_exception.hh"
+
 #include "backend/cpu_policies_gatekeeper.hh"
 #include "backend/cpu_policy.hh"
 #include "backend/cpu_policy_manager.hh"
@@ -38,6 +43,7 @@
 #include "backend/serializer.hh"
 
 #include <gdkmm/pixbuf.h>
+#include <glibmm/markup.h>
 #include <glibmm/timer.h>
 #include <glibmm/ustring.h>
 #include <gtkmm/aboutdialog.h>
@@ -329,7 +335,9 @@ SimulationController::on_simulation_run()
   _toolbt_stop->set_sensitive(true);
 
   _break_requested = false;
-  _sim.run();
+  // Used instead of simply calling "_sim.run()" to
+  // have exception handling only in one place:
+  run_simulation_adaptor();
 }
 
 
@@ -405,7 +413,55 @@ SimulationController::update(const Simulation& simulation)
 bool
 SimulationController::run_simulation_adaptor()
 {
+  using Gtk::MessageDialog;
+  using namespace Glib;
+
   if(!_break_requested)
-    _sim.run();
+    try 
+      {
+        _sim.run();
+      }
+    catch(const UserInterruptException& uie)
+      {
+        // Show the user a dialog
+        MessageDialog diag(_("<b>The selected user CPU policy stopped before returning:</b>\n") + Markup::escape_text(uie.what()), 
+                           true, Gtk::MESSAGE_ERROR, Gtk::BUTTONS_OK, true);
+        diag.run();
+      }
+    catch(const MalformedPolicyException& mpe)
+      {
+        // Show user a dialog
+        MessageDialog diag(_("<b>The selected user CPU policy was malformed and didn't run:</b>\n") + Markup::escape_text(mpe.what()), 
+                           true, Gtk::MESSAGE_ERROR, Gtk::BUTTONS_OK, true);
+        diag.run();
+   
+        try
+          {
+            // Deactivate the policy
+            _sim.set_policy(NULL);
+          }
+        catch(const CPUPolicyException& cpe)
+          {
+            // Fatal error. We should never get here.
+            std::cerr << _(" [EE] Fatal error. Impossible to deactivate the policy in ") <<  __FILE__ << ":" << __LINE__
+                      << std::endl << _(" [EE] ") << cpe.what() << std::endl;
+                                                                                                                      ;
+            abort();
+          }
+      }
+    catch(const NullPolicyException& npe)
+      {
+        MessageDialog diag(_("<b>No active policy selected:</b>\n") + Markup::escape_text(npe.what()), 
+                           true, Gtk::MESSAGE_ERROR, Gtk::BUTTONS_OK, true);
+        diag.run();
+        
+      }
+    catch(const CPUPolicyException& cpe)
+      {
+       MessageDialog diag(_("<b>Unexpected error</b>:\n") + Markup::escape_text(cpe.what()), 
+                           true, Gtk::MESSAGE_ERROR, Gtk::BUTTONS_OK, true);
+        diag.run();
+      }
+
   return false;
 }