diff --git a/src/mlpack/methods/reinforcement_learning/environment/pendulum.hpp b/src/mlpack/methods/reinforcement_learning/environment/pendulum.hpp
index 69e3749faf..bfd4cb1105 100644
--- a/src/mlpack/methods/reinforcement_learning/environment/pendulum.hpp
+++ b/src/mlpack/methods/reinforcement_learning/environment/pendulum.hpp
@@ -82,7 +82,7 @@ class Pendulum
    */
   struct Action
   {
-    double action;
+    double action = 0.0;
     // Storing degree of freedom
     const int size = 1;
   };