diff --git a/include/etl/atomic.h b/include/etl/atomic.h
index b3a556a5..c2b693e5 100644
--- a/include/etl/atomic.h
+++ b/include/etl/atomic.h
@@ -32,7 +32,7 @@ SOFTWARE.
 #include "platform.h"
 
 #if ETL_HAS_ATOMIC
-  #if (ETL_USING_CPP11 && (ETL_USING_STL || defined(ETL_IN_UNIT_TEST)))
+  #if (ETL_USING_CPP11 && ETL_USING_STL)
     #include "atomic/atomic_std.h"
   #elif defined(ETL_COMPILER_ARM5)
     #include "atomic/atomic_arm.h"
diff --git a/include/etl/atomic/atomic_gcc_sync.h b/include/etl/atomic/atomic_gcc_sync.h
index 087489aa..0854e8bf 100644
--- a/include/etl/atomic/atomic_gcc_sync.h
+++ b/include/etl/atomic/atomic_gcc_sync.h
@@ -118,12 +118,12 @@ namespace etl
   {
   public:
 
-    atomic()
+    ETL_CONSTEXPR atomic()
       : value(T())
     {
     }
 
-    atomic(T v)
+    ETL_CONSTEXPR atomic(T v)
       : value(v)
     {
     }
@@ -410,7 +410,7 @@ namespace etl
   {
   public:
 
-    atomic()
+    ETL_CONSTEXPR atomic()
       : value(0U)
     {
     }
@@ -656,12 +656,12 @@ namespace etl
   {
   public:
 
-    atomic()
+    ETL_CONSTEXPR atomic()
       : value(0U)
     {
     }
 
-    atomic(bool v)
+    ETL_CONSTEXPR atomic(bool v)
       : value(char(v))
     {
     }
@@ -997,12 +997,12 @@ namespace etl
 
     ETL_STATIC_ASSERT(etl::is_integral<T>::value, "Only integral types are supported");
 
-    atomic()
+    ETL_CONSTEXPR atomic()
       : value(0)
     {
     }
 
-    atomic(T v)
+    ETL_CONSTEXPR atomic(T v)
       : value(v)
     {
     }
@@ -1401,7 +1401,7 @@ namespace etl
   {
   public:
 
-    atomic()
+    ETL_CONSTEXPR atomic()
       : value(0U)
     {
     }
@@ -1711,12 +1711,12 @@ namespace etl
   {
   public:
 
-    atomic()
+    ETL_CONSTEXPR atomic()
       : value(0U)
     {
     }
 
-    atomic(bool v)
+    ETL_CONSTEXPR atomic(bool v)
       : value(char(v))
     {
     }
diff --git a/include/etl/platform.h b/include/etl/platform.h
index a9918b24..d32afbc9 100644
--- a/include/etl/platform.h
+++ b/include/etl/platform.h
@@ -567,14 +567,14 @@ typedef uint_least32_t char32_t;
   #define ETL_HAS_ATOMIC                  0
   #define ETL_HAS_ATOMIC_ALWAYS_LOCK_FREE 0
 #else
-  #if ((ETL_USING_CPP11 && (ETL_USING_STL || defined(ETL_IN_UNIT_TEST))) || defined(ETL_COMPILER_ARM5) || defined(ETL_COMPILER_ARM6) \
-       || defined(ETL_COMPILER_GCC) || defined(ETL_COMPILER_CLANG))
+  #if ((ETL_USING_CPP11 && ETL_USING_STL) || defined(ETL_COMPILER_ARM5) || defined(ETL_COMPILER_ARM6) || defined(ETL_COMPILER_GCC) \
+       || defined(ETL_COMPILER_CLANG))
     #define ETL_HAS_ATOMIC 1
   #else
     #define ETL_HAS_ATOMIC 0
   #endif
-  #if ((ETL_USING_CPP17 && (ETL_USING_STL || defined(ETL_IN_UNIT_TEST))) || defined(ETL_COMPILER_ARM5) || defined(ETL_COMPILER_ARM6) \
-       || defined(ETL_COMPILER_GCC) || defined(ETL_COMPILER_CLANG))
+  #if ((ETL_USING_CPP17 && ETL_USING_STL) || defined(ETL_COMPILER_ARM5) || defined(ETL_COMPILER_ARM6) || defined(ETL_COMPILER_GCC) \
+       || defined(ETL_COMPILER_CLANG))
     #define ETL_HAS_ATOMIC_ALWAYS_LOCK_FREE 1
   #else
     #define ETL_HAS_ATOMIC_ALWAYS_LOCK_FREE 0
diff --git a/test/test_atomic.cpp b/test/test_atomic.cpp
index 2128332b..039aef2b 100644
--- a/test/test_atomic.cpp
+++ b/test/test_atomic.cpp
@@ -891,5 +891,37 @@ namespace
       CHECK_EQUAL(0, atomic_value.load());
     }
 #endif
+
+#if ETL_USING_CPP11
+    //*************************************************************************
+    TEST(test_atomic_trivial_constexpr_default_constructor)
+    {
+      // Verify that default constructors are usable in constexpr context
+      constexpr etl::atomic<int>  a_int{};
+      constexpr etl::atomic<char> a_char{};
+      constexpr etl::atomic<bool> a_bool{};
+
+      (void)a_int;
+      (void)a_char;
+      (void)a_bool;
+
+      CHECK(true);
+    }
+
+    //*************************************************************************
+    TEST(test_atomic_trivial_constexpr_value_constructor)
+    {
+      // Verify that value constructors are usable in constexpr context
+      constexpr etl::atomic<int>  a_int{42};
+      constexpr etl::atomic<char> a_char{'A'};
+      constexpr etl::atomic<bool> a_bool{true};
+
+      (void)a_int;
+      (void)a_char;
+      (void)a_bool;
+
+      CHECK(true);
+    }
+#endif
   }
 } // namespace
diff --git a/test/test_message_timer_atomic.cpp b/test/test_message_timer_atomic.cpp
index 6cc94520..768bdf72 100644
--- a/test/test_message_timer_atomic.cpp
+++ b/test/test_message_timer_atomic.cpp
@@ -37,11 +37,13 @@ SOFTWARE.
 #include <thread>
 #include <vector>
 
-#if defined(ETL_COMPILER_MICROSOFT)
-  #include <Windows.h>
-#endif
+#if ETL_HAS_ATOMIC
 
-#define REALTIME_TEST 0
+  #if defined(ETL_COMPILER_MICROSOFT)
+    #include <Windows.h>
+  #endif
+
+  #define REALTIME_TEST 0
 
 //***************************************************************************
 // The set of messages.
@@ -130,7 +132,7 @@ namespace
   Router1 router1;
   Bus1    bus1;
 
-  using event_callback_type = etl::imessage_timer_atomic<std::atomic_uint32_t>::event_callback_type;
+  using event_callback_type = etl::imessage_timer_atomic<etl::atomic_uint32_t>::event_callback_type;
 
   class TimerInsertRemoveTest
   {
@@ -170,7 +172,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_too_many_timers)
     {
-      etl::message_timer_atomic<2, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<2, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Single_Shot);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Single_Shot);
@@ -188,7 +190,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_one_shot)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Single_Shot);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Single_Shot);
@@ -224,7 +226,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_one_shot_after_timeout)
     {
-      etl::message_timer_atomic<1, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<1, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Single_Shot);
       router1.clear();
@@ -270,7 +272,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_repeating)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Repeating);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -306,7 +308,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_repeating_bigger_step)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Repeating);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -346,7 +348,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_repeating_stop_start)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Repeating);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -393,7 +395,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_repeating_register_unregister)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1;
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -436,7 +438,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_repeating_clear)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Repeating);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -478,7 +480,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_route_through_bus)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, bus1, 37, etl::timer::mode::Single_Shot, ROUTER1);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, bus1, 23, etl::timer::mode::Single_Shot, ROUTER1);
@@ -517,7 +519,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_immediate_delayed)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Repeating);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -558,7 +560,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_one_shot_big_step_short_delay_insert)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 15, etl::timer::mode::Single_Shot);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 5, etl::timer::mode::Repeating);
@@ -590,7 +592,7 @@ namespace
     //*************************************************************************
     TEST(callback_timer_one_shot_empty_list_huge_tick_before_insert)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 5, etl::timer::mode::Single_Shot);
 
@@ -628,7 +630,7 @@ namespace
     //*************************************************************************
     TEST(message_timer_time_to_next)
     {
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Repeating);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Repeating);
@@ -679,7 +681,7 @@ namespace
     TEST(message_timer_time_to_next_with_has_active_timer)
     {
       timerInsertRemoveTest.clear();
-      etl::message_timer_atomic<3, std::atomic_uint32_t> timer_controller;
+      etl::message_timer_atomic<3, etl::atomic_uint32_t> timer_controller;
 
       etl::timer::id::type id1 = timer_controller.register_timer(message1, router1, 37, etl::timer::mode::Single_Shot);
       etl::timer::id::type id2 = timer_controller.register_timer(message2, router1, 23, etl::timer::mode::Single_Shot);
@@ -734,18 +736,18 @@ namespace
     }
 
     //*************************************************************************
-#if REALTIME_TEST
+  #if REALTIME_TEST
 
-  #if defined(ETL_TARGET_OS_WINDOWS) // Only Windows priority is currently
-                                     // supported
-    #define RAISE_THREAD_PRIORITY  SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_HIGHEST)
-    #define FIX_PROCESSOR_AFFINITY SetThreadAffinityMask(GetCurrentThread(), 1);
-  #else
-    #define RAISE_THREAD_PRIORITY
-    #define FIX_PROCESSOR_AFFINITY
-  #endif
+    #if defined(ETL_TARGET_OS_WINDOWS) // Only Windows priority is currently
+                                       // supported
+      #define RAISE_THREAD_PRIORITY  SetThreadPriority(GetCurrentThread(), THREAD_PRIORITY_HIGHEST)
+      #define FIX_PROCESSOR_AFFINITY SetThreadAffinityMask(GetCurrentThread(), 1);
+    #else
+      #define RAISE_THREAD_PRIORITY
+      #define FIX_PROCESSOR_AFFINITY
+    #endif
 
-    etl::message_timer_atomic<3, std::atomic_uint32_t> controller;
+    etl::message_timer_atomic<3, etl::atomic_uint32_t> controller;
 
     void timer_event()
     {
@@ -821,6 +823,8 @@ namespace
       CHECK_EQUAL(10U, router1.message2.size());
       CHECK(router1.message2.size() < 65U);
     }
-#endif
+  #endif
   }
 } // namespace
+
+#endif // ETL_HAS_ATOMIC
diff --git a/test/test_shared_message.cpp b/test/test_shared_message.cpp
index b5c5440a..885f0770 100644
--- a/test/test_shared_message.cpp
+++ b/test/test_shared_message.cpp
@@ -36,6 +36,8 @@ SOFTWARE.
 #include "etl/reference_counted_message_pool.h"
 #include "etl/shared_message.h"
 
+#if ETL_HAS_ATOMIC
+
 namespace
 {
   constexpr etl::message_id_t MessageId1 = 1U;
@@ -216,9 +218,9 @@ namespace
 
       etl::atomic_counted_message_pool message_pool(memory_allocator);
 
-#include "etl/private/diagnostic_pessimizing_move_push.h"
+  #include "etl/private/diagnostic_pessimizing_move_push.h"
       etl::shared_message sm(std::move(etl::shared_message(message_pool, Message1())));
-#include "etl/private/diagnostic_pop.h"
+  #include "etl/private/diagnostic_pop.h"
 
       CHECK_EQUAL(1, sm.get_reference_count());
     }
@@ -228,9 +230,9 @@ namespace
     {
       message_1_instantiations = 0;
 
-#include "etl/private/diagnostic_pessimizing_move_push.h"
+  #include "etl/private/diagnostic_pessimizing_move_push.h"
       etl::shared_message sm(std::move(common_message_pool.create_message<Message1>()));
-#include "etl/private/diagnostic_pop.h"
+  #include "etl/private/diagnostic_pop.h"
 
       CHECK_EQUAL(1, sm.get_reference_count());
       CHECK_EQUAL(1, message_1_instantiations);
@@ -239,9 +241,9 @@ namespace
     //*************************************************************************
     TEST(test_move_constructor_with_parametrized_constructed_message)
     {
-#include "etl/private/diagnostic_pessimizing_move_push.h"
+  #include "etl/private/diagnostic_pessimizing_move_push.h"
       etl::shared_message sm(std::move(etl::shared_message(common_message_pool, Message1(1))));
-#include "etl/private/diagnostic_pop.h"
+  #include "etl/private/diagnostic_pop.h"
 
       CHECK_EQUAL(1, sm.get_reference_count());
     }
@@ -251,9 +253,9 @@ namespace
     {
       message_1_instantiations = 0;
 
-#include "etl/private/diagnostic_pessimizing_move_push.h"
+  #include "etl/private/diagnostic_pessimizing_move_push.h"
       etl::shared_message sm(std::move(common_message_pool.create_message<Message1>(1)));
-#include "etl/private/diagnostic_pop.h"
+  #include "etl/private/diagnostic_pop.h"
 
       CHECK_EQUAL(1, sm.get_reference_count());
       CHECK_EQUAL(1, message_1_instantiations);
@@ -298,9 +300,9 @@ namespace
       etl::atomic_counted_message_pool message_pool(memory_allocator);
 
       etl::shared_message sm2 = etl::shared_message(message_pool, Message1(2));
-#include "etl/private/diagnostic_pessimizing_move_push.h"
+  #include "etl/private/diagnostic_pessimizing_move_push.h"
       sm2 = std::move(etl::shared_message(message_pool, Message1(3)));
-#include "etl/private/diagnostic_pop.h"
+  #include "etl/private/diagnostic_pop.h"
       CHECK_EQUAL(1, sm2.get_reference_count());
       CHECK(sm2.is_valid());
     }
@@ -374,3 +376,5 @@ namespace
     }
   }
 } // namespace
+
+#endif // ETL_HAS_ATOMIC
diff --git a/test/test_unordered_map.cpp b/test/test_unordered_map.cpp
index d70b2bc3..fe47e6d4 100644
--- a/test/test_unordered_map.cpp
+++ b/test/test_unordered_map.cpp
@@ -43,6 +43,7 @@ SOFTWARE.
 
 #include "data.h"
 
+#include "etl/char_traits.h"
 #include "etl/hash.h"
 #include "etl/unordered_map.h"
 
diff --git a/test/test_unordered_multimap.cpp b/test/test_unordered_multimap.cpp
index 42d7728c..a48be17d 100644
--- a/test/test_unordered_multimap.cpp
+++ b/test/test_unordered_multimap.cpp
@@ -41,6 +41,7 @@ SOFTWARE.
 
 #include "data.h"
 
+#include "etl/char_traits.h"
 #include "etl/unordered_multimap.h"
 
 namespace etl
diff --git a/test/test_unordered_multiset.cpp b/test/test_unordered_multiset.cpp
index bfa5f3ce..2a3944da 100644
--- a/test/test_unordered_multiset.cpp
+++ b/test/test_unordered_multiset.cpp
@@ -40,6 +40,7 @@ SOFTWARE.
 
 #include "data.h"
 
+#include "etl/char_traits.h"
 #include "etl/checksum.h"
 #include "etl/unordered_multiset.h"
 
diff --git a/test/test_unordered_set.cpp b/test/test_unordered_set.cpp
index b0b7dbd5..60063aa2 100644
--- a/test/test_unordered_set.cpp
+++ b/test/test_unordered_set.cpp
@@ -39,6 +39,7 @@ SOFTWARE.
 
 #include "data.h"
 
+#include "etl/char_traits.h"
 #include "etl/checksum.h"
 #include "etl/hash.h"
 #include "etl/unordered_set.h"