diff --git a/include/etl/fsm.h b/include/etl/fsm.h
index 7618d334..4149d802 100644
--- a/include/etl/fsm.h
+++ b/include/etl/fsm.h
@@ -152,6 +152,9 @@ namespace etl
     }
   };
 
+  //***************************************************************************
+  /// Exception for forbidden state changes.
+  //***************************************************************************
   class fsm_state_enter_state_change_forbidden : public etl::fsm_exception
   {
   public:
diff --git a/include/etl/hfsm.h b/include/etl/hfsm.h
index 24475c40..2738a6a2 100644
--- a/include/etl/hfsm.h
+++ b/include/etl/hfsm.h
@@ -58,13 +58,13 @@ namespace etl
     {
       etl::fsm_state_id_t next_state_id = p_state->process_event(message);
 
-      if(next_state_id != ifsm_state::NO_CHANGE)
+      if (next_state_id != ifsm_state::NO_CHANGE)
       {
         ETL_ASSERT(next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
         etl::ifsm_state* p_next_state = state_list[next_state_id];
 
         // Have we changed state?
-        if(p_next_state != p_state)
+        if (p_next_state != p_state)
         {
           etl::ifsm_state* p_root = common_ancestor(p_state, p_next_state);
           do_exits(p_root, p_state);
@@ -72,7 +72,8 @@ namespace etl
           p_state = p_next_state;
           
           next_state_id = do_enters(p_root, p_next_state, true);
-          if(next_state_id != ifsm_state::NO_CHANGE)
+
+          if (next_state_id != ifsm_state::NO_CHANGE)
           {
             ETL_ASSERT(next_state_id < number_of_states, ETL_ERROR(etl::fsm_state_id_exception));
             p_state = state_list[next_state_id];
@@ -81,11 +82,16 @@ namespace etl
       }
     }
 
+  private:
+
+    //*******************************************
+    /// Return the common ancester of the two states.
+    //*******************************************
     static etl::ifsm_state* common_ancestor(etl::ifsm_state* p_one, etl::ifsm_state* p_two)
     {
-      if(p_one == p_two)
+      if (p_one == p_two)
       {
-          return p_one;
+        return p_one;
       }
 
       etl::ifsm_state* p_current_state = p_one;
@@ -100,7 +106,7 @@ namespace etl
         p_current_state = p_current_state->p_parent;
       }
 
-      if(p_two->p_parent != ETL_NULLPTR)
+      if (p_two->p_parent != ETL_NULLPTR)
       {
         return common_ancestor(p_one, p_two->p_parent);
       }
@@ -108,6 +114,9 @@ namespace etl
       return ETL_NULLPTR;
     }
 
+    //*******************************************
+    /// Exiting the state.
+    //*******************************************
     static void do_exits(const etl::ifsm_state* p_root, etl::ifsm_state* p_source)
     {
       etl::ifsm_state* p_current = p_source;
@@ -126,6 +135,9 @@ namespace etl
       }
     }
 
+    //*******************************************
+    /// Entering the state.
+    //*******************************************
     static etl::fsm_state_id_t do_enters(const etl::ifsm_state* p_root, etl::ifsm_state* p_target, bool activate_default_children)
     {
       ETL_ASSERT(p_target != ETL_NULLPTR, ETL_ERROR(etl::fsm_null_state_exception));
@@ -133,7 +145,7 @@ namespace etl
       // We need to go recursively up the tree if the target and root don't match
       if (p_root != p_target && p_target->p_parent != ETL_NULLPTR)
       {
-        if(p_target->p_parent != p_root)
+        if (p_target->p_parent != p_root)
         {
           // The parent we're calling shouldn't activate its defaults, or this state will be deactivated.
           do_enters(p_root, p_target->p_parent, false);
@@ -156,6 +168,7 @@ namespace etl
           next_state = p_target->on_enter_state();
           ETL_ASSERT(ifsm_state::NO_CHANGE == next_state, ETL_ERROR(etl::fsm_state_enter_state_change_forbidden));
         }
+
         next_state = p_target->get_state_id();
       }
 
diff --git a/test/vs2019/etl.vcxproj b/test/vs2019/etl.vcxproj
index 37f1980a..80c7a26d 100644
--- a/test/vs2019/etl.vcxproj
+++ b/test/vs2019/etl.vcxproj
@@ -1326,6 +1326,7 @@
     <ClInclude Include="..\..\include\etl\generators\type_traits_generator.h" />
     <ClInclude Include="..\..\include\etl\generators\variant_pool_generator.h" />
     <ClInclude Include="..\..\include\etl\generic_pool.h" />
+    <ClInclude Include="..\..\include\etl\hfsm.h" />
     <ClInclude Include="..\..\include\etl\histogram.h" />
     <ClInclude Include="..\..\include\etl\imemory_block_allocator.h" />
     <ClInclude Include="..\..\include\etl\indirect_vector.h" />
@@ -4481,6 +4482,7 @@
     <ClCompile Include="..\test_forward_list_shared_pool.cpp" />
     <ClCompile Include="..\test_bit_stream.cpp" />
     <ClCompile Include="..\test_gamma.cpp" />
+    <ClCompile Include="..\test_hfsm.cpp" />
     <ClCompile Include="..\test_histogram.cpp" />
     <ClCompile Include="..\test_indirect_vector.cpp" />
     <ClCompile Include="..\test_indirect_vector_external_buffer.cpp" />
diff --git a/test/vs2019/etl.vcxproj.filters b/test/vs2019/etl.vcxproj.filters
index a2429199..8b11f5cf 100644
--- a/test/vs2019/etl.vcxproj.filters
+++ b/test/vs2019/etl.vcxproj.filters
@@ -1098,6 +1098,9 @@
     <ClInclude Include="..\..\include\etl\rescale.h">
       <Filter>ETL\Maths</Filter>
     </ClInclude>
+    <ClInclude Include="..\..\include\etl\hfsm.h">
+      <Filter>ETL\Frameworks</Filter>
+    </ClInclude>
   </ItemGroup>
   <ItemGroup>
     <ClCompile Include="..\main.cpp">
@@ -2513,6 +2516,9 @@
     <ClCompile Include="..\test_atomic_gcc_sync.cpp">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\test_hfsm.cpp">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <None Include="..\..\library.properties">