diff --git a/unsupported/Eigen/CXX11/src/Tensor/TensorTrace.h b/unsupported/Eigen/CXX11/src/Tensor/TensorTrace.h
index f2a6c5fcd..25f8ff003 100644
--- a/unsupported/Eigen/CXX11/src/Tensor/TensorTrace.h
+++ b/unsupported/Eigen/CXX11/src/Tensor/TensorTrace.h
@@ -136,6 +136,7 @@ struct TensorEvaluator<const TensorTraceOp<Dims, ArgType>, Device>
       }
     }
 
+    EIGEN_ONLY_USED_FOR_DEBUG(num_distinct_reduce_dims);
     eigen_assert(num_distinct_reduce_dims == NumReducedDims);
 
     // Compute the dimensions of the result.