diff --git a/src/emucore/Genesis.cxx b/src/emucore/Genesis.cxx
index 24a6d4fd0..f5da509db 100644
--- a/src/emucore/Genesis.cxx
+++ b/src/emucore/Genesis.cxx
@@ -30,7 +30,7 @@ Genesis::Genesis(Jack jack, const Event& event, const System& system)
     myLeftEvent    = Event::JoystickZeroLeft;
     myRightEvent   = Event::JoystickZeroRight;
     myFire1Event   = Event::JoystickZeroFire1;
-    myFire2Event   = Event::JoystickZeroFire2;
+    myFire2Event   = Event::JoystickZeroFire3;
   }
   else
   {
@@ -39,11 +39,12 @@ Genesis::Genesis(Jack jack, const Event& event, const System& system)
     myLeftEvent    = Event::JoystickOneLeft;
     myRightEvent   = Event::JoystickOneRight;
     myFire1Event   = Event::JoystickOneFire1;
-    myFire2Event   = Event::JoystickOneFire2;
+    myFire2Event   = Event::JoystickOneFire3;
   }
 
   // Analog pin 9 is not connected to this controller at all
-  // Analog pin 5 corresponds to button 'C' on the gamepad
+  // Analog pin 5 corresponds to button 'C' on the gamepad, and corresponds
+  // to the 'booster' button on a BoosterGrip controller
   myAnalogPinValue[Five] = myAnalogPinValue[Nine] = maximumResistance;
 }
 
diff --git a/src/emucore/Genesis.hxx b/src/emucore/Genesis.hxx
index a58a90cf7..a21e90b2e 100644
--- a/src/emucore/Genesis.hxx
+++ b/src/emucore/Genesis.hxx
@@ -27,7 +27,8 @@
   The standard Sega Genesis controller works with the 2600 console for
   joystick directions and some of the buttons.  Button 'B' corresponds to
   the normal fire button (joy0fire), while button 'C' is read through
-  INPT1 (analog pin 5), which is normally mapped to the BoosterGrip trigger.
+  INPT1 (analog pin 5), which is normally mapped to the BoosterGrip
+  booster button.
 
   @author  Stephen Anthony
 */