diff --git a/Tracking/TrkFitter/TrkGaussianSumFilter/TrkGaussianSumFilter/GsfExtrapolator.h b/Tracking/TrkFitter/TrkGaussianSumFilter/TrkGaussianSumFilter/GsfExtrapolator.h
index 8db31e2430a36034a5fa861ef841bc2f2ec40fa9..65b36f5be2c1f1ef7ab08bf23538a8c2a2bf4233 100644
--- a/Tracking/TrkFitter/TrkGaussianSumFilter/TrkGaussianSumFilter/GsfExtrapolator.h
+++ b/Tracking/TrkFitter/TrkGaussianSumFilter/TrkGaussianSumFilter/GsfExtrapolator.h
@@ -48,7 +48,7 @@ class IMaterialMixtureConvolution;
 class IMultipleScatteringUpdator;
 /** @class GsfExtrapolator */
 
-class GsfExtrapolator
+class GsfExtrapolator final
   : public AthAlgTool
   , virtual public IMultiStateExtrapolator
 {