diff --git a/include/asyncpp/timer/delay.inl b/include/asyncpp/timer/delay.inl
index 3bbd614..e5c2741 100644
--- a/include/asyncpp/timer/delay.inl
+++ b/include/asyncpp/timer/delay.inl
@@ -19,7 +19,8 @@ namespace timer {
 
     template<typename T_base, typename T_ratio>
     delay::delay(const duration<T_base, T_ratio>& p_duration)
-        : _timeout(clock::now() + p_duration)
+        : _timeout      (clock::now() + p_duration)
+        , _registration (*this)
         { }
 
     inline delay::~delay()
diff --git a/include/asyncpp/timer/timer.h b/include/asyncpp/timer/timer.h
index 17ebb1f..77c1e4a 100644
--- a/include/asyncpp/timer/timer.h
+++ b/include/asyncpp/timer/timer.h
@@ -3,6 +3,8 @@
 #include <set>
 #include <memory>
 
+#include <cppcore/synchronization/locked.h>
+
 #include "misc.h"
 
 namespace asyncpp {
@@ -48,7 +50,13 @@ namespace timer {
         using inner_set = std::set<inner_ptr_s, inner_less_compare>;
 
     private:
-        inner_set _registrations;
+        cppcore::locked<inner_set> _registrations;
+
+    public:
+        /**
+         * @brief Constructor.
+         */
+        inline ~timer();
 
     public:
         /**
diff --git a/include/asyncpp/timer/timer.inl b/include/asyncpp/timer/timer.inl
index fd51be9..65def8d 100644
--- a/include/asyncpp/timer/timer.inl
+++ b/include/asyncpp/timer/timer.inl
@@ -35,8 +35,15 @@ namespace timer {
 
     /* timer */
 
+    timer::~timer()
+    {
+        auto& s = local_storage();
+        if (s.current == this)
+            s.current = nullptr;
+    }
+
     size_t timer::resource_count() const
-        { return _registrations.size(); }
+        { return _registrations.lock()->size(); }
 
     void timer::make_current()
     {
@@ -83,13 +90,13 @@ namespace timer {
         auto s = p_value.ptr.lock();
         p_value.ptr.reset();
         if (s)
-            s->owner._registrations.erase(s);
+            s->owner._registrations.lock()->erase(s);
     }
 
     inline timer::inner_ptr_s timer::make_inner(registration& p_value)
     {
         auto s = std::make_shared<registration::inner>(*this, p_value.owner.timeout());
-        _registrations.insert(s);
+        _registrations.lock()->insert(s);
         return s;
     }
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 6c607fc..afd6aa9 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -4,6 +4,8 @@ Include                             ( cotire        OPTIONAL RESULT_VARIABLE HAS
 Include                             ( pedantic      OPTIONAL RESULT_VARIABLE HAS_PEDANTIC )
 Include                             ( strip_symbols OPTIONAL RESULT_VARIABLE HAS_STRIP_SYMBOLS )
 
+Find_Package                        ( cppcore REQUIRED )
+
 # Interface Library ###############################################################################
 
 Set                                 ( ASYNCPP_INCLUDE_DIR ${CMAKE_CURRENT_SOURCE_DIR}/../include )
@@ -12,6 +14,9 @@ Target_Include_Directories          ( asyncpp
                                       INTERFACE
                                         $<BUILD_INTERFACE:${ASYNCPP_INCLUDE_DIR}>
                                         $<INSTALL_INTERFACE:${ASYNCPP_INSTALL_DIR_INCLUDE}> )
+Target_Link_Libraries               ( asyncpp
+                                      INTERFACE
+                                        cppcore::cppcore )
 
 # Install #########################################################################################
 
diff --git a/test/asyncpp/timer/timer_tests.cpp b/test/asyncpp/timer/timer_tests.cpp
new file mode 100644
index 0000000..1c3279d
--- /dev/null
+++ b/test/asyncpp/timer/timer_tests.cpp
@@ -0,0 +1,78 @@
+#include <gtest/gtest.h>
+
+#include "../../helper/now_mock.h"
+
+#include <asyncpp.h>
+#include <asyncpp/timer.h>
+
+using namespace ::testing;
+using namespace ::asyncpp;
+
+TEST(timer_tests, current)
+{
+    {
+    timer::timer t;
+
+    EXPECT_EQ(nullptr, timer::timer::current());
+
+    t.make_current();
+
+    EXPECT_EQ(&t, timer::timer::current());
+
+    t.clear_current();
+
+    EXPECT_EQ(nullptr, timer::timer::current());
+
+    t.make_current();
+
+    EXPECT_EQ(&t, timer::timer::current());
+    }
+
+    EXPECT_EQ(nullptr, timer::timer::current());
+}
+
+TEST(timer_tests, resource_registration)
+{
+    StrictMock<now_mock> m;
+    EXPECT_CALL(m, now)
+        .WillRepeatedly(Return(timer::time_point(std::chrono::seconds(0))));
+
+    using delay_future_type = decltype(as_future(timer::delay(std::chrono::seconds(10))));
+
+    timer::timer t;
+    t.make_current();
+
+    auto f1 = std::make_unique<delay_future_type>(timer::delay(std::chrono::seconds(10)));
+    auto f2 = std::make_unique<delay_future_type>(timer::delay(std::chrono::seconds(20)));
+    auto f3 = std::make_unique<delay_future_type>(timer::delay(std::chrono::seconds(30)));
+
+    EXPECT_EQ(0, t.resource_count());
+
+    f1->poll(); // simple add
+
+    EXPECT_EQ(1, t.resource_count());
+
+    f2->poll(); // simple add
+
+    EXPECT_EQ(2, t.resource_count());
+
+    f1.reset(); // remove first
+
+    EXPECT_EQ(1, t.resource_count());
+
+    f3->poll(); // simple add
+
+    EXPECT_EQ(2, t.resource_count());
+
+    f3->poll(); // calling twice should not add
+
+    EXPECT_EQ(2, t.resource_count());
+
+    f3.reset(); // remove last
+
+    EXPECT_EQ(1, t.resource_count());
+
+    f2.reset(); // remove remaining
+
+    EXPECT_EQ(0, t.resource_count());
+}