diff --git a/src/mlpack/methods/ann/layer/linear3d.hpp b/src/mlpack/methods/ann/layer/linear3d.hpp
index b248b450b1..618c0bf304 100644
--- a/src/mlpack/methods/ann/layer/linear3d.hpp
+++ b/src/mlpack/methods/ann/layer/linear3d.hpp
@@ -90,7 +90,7 @@ class Linear3DType : public Layer<MatType>
    * @param g The calculated gradient.
    */
   void Backward(const MatType& /* input */,
-                const MatType& output,
+                const MatType& /* output */,
                 const MatType& gy,
                 MatType& g);