diff --git a/src/mlpack/methods/reinforcement_learning/environment/CMakeLists.txt b/src/mlpack/methods/reinforcement_learning/environment/CMakeLists.txt
index be5d1f3486..77d822aced 100644
--- a/src/mlpack/methods/reinforcement_learning/environment/CMakeLists.txt
+++ b/src/mlpack/methods/reinforcement_learning/environment/CMakeLists.txt
@@ -2,7 +2,6 @@
 # Anything not in this list will not be compiled into mlpack.
 set(SOURCES
   env_type.hpp
-  env_type.cpp
   mountain_car.hpp
   cart_pole.hpp
   continuous_mountain_car.hpp
diff --git a/src/mlpack/methods/reinforcement_learning/environment/env_type.cpp b/src/mlpack/methods/reinforcement_learning/environment/env_type.cpp
deleted file mode 100644
index 98f0799199..0000000000
--- a/src/mlpack/methods/reinforcement_learning/environment/env_type.cpp
+++ /dev/null
@@ -1,29 +0,0 @@
-/**
- * @file methods/reinforcement_learning/environment/env_type.cpp
- * @author Nishant Kumar
- *
- * This file defines the static variables used by the discrete and continuous
- * environments.
- *
- * mlpack is free software; you may redistribute it and/or modify it under the
- * terms of the 3-clause BSD license.  You should have received a copy of the
- * 3-clause BSD license along with mlpack.  If not, see
- * http://www.opensource.org/licenses/BSD-3-Clause for more information.
- */
-#include "env_type.hpp"
-
-namespace mlpack {
-namespace rl {
-
-// Instantiate static members.
-
-size_t DiscreteActionEnv::State::dimension = 0;
-size_t DiscreteActionEnv::Action::size = 0;
-size_t DiscreteActionEnv::rewardSize = 0;
-
-size_t ContinuousActionEnv::State::dimension = 0;
-size_t ContinuousActionEnv::Action::size = 0;
-size_t ContinuousActionEnv::rewardSize = 0;
-
-} // namespace rl
-} // namespace mlpack
diff --git a/src/mlpack/methods/reinforcement_learning/environment/env_type.hpp b/src/mlpack/methods/reinforcement_learning/environment/env_type.hpp
index 46a4c746bf..98bd8963b9 100644
--- a/src/mlpack/methods/reinforcement_learning/environment/env_type.hpp
+++ b/src/mlpack/methods/reinforcement_learning/environment/env_type.hpp
@@ -206,6 +206,19 @@ class ContinuousActionEnv
   static size_t rewardSize;
 };
 
+#ifndef MLPACK_METHODS_RL_ENVIRONMENT_ENV_TYPE_VARIABLES
+#define MLPACK_METHODS_RL_ENVIRONMENT_ENV_TYPE_VARIABLES
+
+size_t DiscreteActionEnv::State::dimension = 0;
+size_t DiscreteActionEnv::Action::size = 0;
+size_t DiscreteActionEnv::rewardSize = 0;
+
+size_t ContinuousActionEnv::State::dimension = 0;
+size_t ContinuousActionEnv::Action::size = 0;
+size_t ContinuousActionEnv::rewardSize = 0;
+
+#endif
+
 } // namespace rl
 } // namespace mlpack