diff --git a/src/cpu/o3/scoreboard.hh b/src/cpu/o3/scoreboard.hh
index 1012bae595..f09b195404 100644
--- a/src/cpu/o3/scoreboard.hh
+++ b/src/cpu/o3/scoreboard.hh
@@ -61,7 +61,7 @@ class Scoreboard
     std::vector<bool> regScoreBoard;
 
     /** The number of actual physical registers */
-    unsigned numPhysRegs;
+    unsigned M5_CLASS_VAR_USED numPhysRegs;
 
   public:
     /** Constructs a scoreboard.