diff --git a/src/mlpack/methods/ann/activation_functions/elish_function.hpp b/src/mlpack/methods/ann/activation_functions/elish_function.hpp
index 8f13b00a7c..4eced57122 100644
--- a/src/mlpack/methods/ann/activation_functions/elish_function.hpp
+++ b/src/mlpack/methods/ann/activation_functions/elish_function.hpp
@@ -111,11 +111,16 @@ class ElishFunction
   {
     // simplified the x>=0 part to be in terms of x and y -- maybe
     // the x<0 part can be as well?
+    dy.set_size(arma::size(y));
     arma::uvec ltz = arma::find(x < 0);
-    InputVecType ex = arma::exp(x(ltz));
-    dy(ltz) = (ex - 2 / (1 + ex) + 2 / arma::pow(1 + ex, 2));
+    if (!ltz.empty()) {
+      InputVecType ex = arma::exp(x(ltz));
+      dy(ltz) = (ex - 2 / (1 + ex) + 2 / arma::pow(1 + ex, 2));
+    }
     arma::uvec gtz = arma::find(x > 0);
-    dy(gtz) = (y(gtz) / x(gtz)) % (1.0 + x(gtz) - y(gtz));
+    if (!gtz.empty()) {
+      dy(gtz) = (y(gtz) / x(gtz)) % (1.0 + x(gtz) - y(gtz));
+    }
     dy(arma::find(x == 0)).fill(0.5);
     // the expression above is indeterminate at 0, even though
     // the expression solely in terms of x is defined (= 0.5)