diff --git a/src/SystemContainer.hpp b/src/SystemContainer.hh
similarity index 89%
rename from src/SystemContainer.hpp
rename to src/SystemContainer.hh
index 6027b05926..45ed26d231 100644
--- a/src/SystemContainer.hpp
+++ b/src/SystemContainer.hh
@@ -22,10 +22,13 @@
 #include <cstddef>
 #include <functional>
 
+#include "gz/sim/config.hh"
+
 namespace gz
 {
   namespace sim
   {
+    inline namespace GZ_SIM_VERSION_NAMESPACE {
     //////////////////////////////////////////////////
     /// This container implements a simple masked vector.
     /// Using a masked vector for systems ensures that
@@ -103,7 +106,7 @@ namespace gz
       private: std::vector<std::size_t> freeSpots;
 
       //////////////////////////////////////////
-      class iterator {
+      class Iterator {
         std::size_t num;
         SystemContainer<T>* parent;
       public:
@@ -112,12 +115,12 @@ namespace gz
         using difference_type = long;
         using pointer = T*;
         using reference = T&;
-        explicit iterator(SystemContainer<T>* _parent, std::size_t _num = 0) :
+        explicit Iterator(SystemContainer<T>* _parent, std::size_t _num = 0) :
           num(_num), parent(_parent)
         {
 
         }
-        iterator& operator++() {
+        Iterator& operator++() {
           auto end = parent->end();
           // O(n) for now
           do {
@@ -126,36 +129,37 @@ namespace gz
 
           return *this;
         }
-        bool operator==(iterator other) const { return num == other.num; }
-        bool operator!=(iterator other) const { return !(*this == other); }
+        bool operator==(Iterator other) const { return num == other.num; }
+        bool operator!=(Iterator other) const { return !(*this == other); }
         T& operator*() const {
           return parent->systems[num];
         }
       };
 
       //////////////////////////////////////////
-      public: iterator begin()
+      public: Iterator begin()
       {
-        return iterator(this);
+        return Iterator(this);
       }
 
       //////////////////////////////////////////
-      public: iterator end()
+      public: Iterator end()
       {
         auto lastIdx = this->occupied.size();
 
         if (lastIdx == 0)
         {
-          return iterator(this);
+          return Iterator(this);
         }
 
         while(!this->occupied[lastIdx-1] && lastIdx != 0)
         {
           lastIdx--;
         }
-        return iterator(this, lastIdx);
+        return Iterator(this, lastIdx);
       }
     };
+    }
   }
 }
 
diff --git a/src/SystemContainer_TEST.cc b/src/SystemContainer_TEST.cc
index c002913de3..857b29af26 100644
--- a/src/SystemContainer_TEST.cc
+++ b/src/SystemContainer_TEST.cc
@@ -16,7 +16,7 @@
 */
 #include <gtest/gtest.h>
 #include <unordered_set>
-#include "SystemContainer.hpp"
+#include "SystemContainer.hh"
 
 using namespace gz::sim;
 
diff --git a/src/SystemManager.cc b/src/SystemManager.cc
index b9f7c518b1..86628965f5 100644
--- a/src/SystemManager.cc
+++ b/src/SystemManager.cc
@@ -22,7 +22,7 @@
 
 #include <gz/common/StringUtils.hh>
 
-#include "SystemContainer.hpp"
+#include "SystemContainer.hh"
 #include "SystemInternal.hh"
 #include "gz/sim/components/SystemPluginInfo.hh"
 #include "gz/sim/Conversions.hh"
diff --git a/src/SystemManager.hh b/src/SystemManager.hh
index 4b1ff39717..430a9f2fb3 100644
--- a/src/SystemManager.hh
+++ b/src/SystemManager.hh
@@ -34,7 +34,7 @@
 #include "gz/sim/SystemLoader.hh"
 #include "gz/sim/Types.hh"
 
-#include "SystemContainer.hpp"
+#include "SystemContainer.hh"
 #include "SystemInternal.hh"
 
 namespace gz