diff --git a/repos/os/src/drivers/timer/include/threaded_time_source.h b/repos/os/src/drivers/timer/include/threaded_time_source.h
index fa13aaeaf9..a640b8f029 100644
--- a/repos/os/src/drivers/timer/include/threaded_time_source.h
+++ b/repos/os/src/drivers/timer/include/threaded_time_source.h
@@ -35,7 +35,7 @@ class Timer::Threaded_time_source : public Genode::Time_source,
 
 		struct Irq_dispatcher
 		{
-			GENODE_RPC(Rpc_do_dispatch, void, do_dispatch, Duration);
+			GENODE_RPC(Rpc_do_dispatch, void, do_dispatch);
 			GENODE_RPC_INTERFACE(Rpc_do_dispatch);
 		};
 
@@ -43,16 +43,23 @@ class Timer::Threaded_time_source : public Genode::Time_source,
 		                                                     Irq_dispatcher_component>
 		{
 				Timeout_handler *handler = nullptr;
+				Threaded_time_source &ts;
 
+				Irq_dispatcher_component(Threaded_time_source &ts) : ts(ts) { }
 
 				/********************
 				 ** Irq_dispatcher **
 				 ********************/
 
-				void do_dispatch(Duration curr_time)
+				void do_dispatch()
 				{
-					if (handler) {
-						handler->handle_timeout(Duration(curr_time)); }
+					/* call curr_time in ep and not in ts (no locks in use!) */
+					ts._irq = true;
+					Duration us = ts.curr_time();
+					ts._irq = false;
+
+					if (handler)
+						handler->handle_timeout(us);
 				}
 
 		} _irq_dispatcher_component;
@@ -61,7 +68,6 @@ class Timer::Threaded_time_source : public Genode::Time_source,
 
 		virtual void _wait_for_irq() = 0;
 
-
 		/***********************
 		 ** Thread_deprecated **
 		 ***********************/
@@ -70,15 +76,20 @@ class Timer::Threaded_time_source : public Genode::Time_source,
 		{
 			while (true) {
 				_wait_for_irq();
-				_irq_dispatcher_cap.call<Irq_dispatcher::Rpc_do_dispatch>(curr_time());
+				_irq_dispatcher_cap.call<Irq_dispatcher::Rpc_do_dispatch>();
 			}
 		}
 
+	protected:
+
+		bool _irq { false };
+
 	public:
 
 		Threaded_time_source(Genode::Env &env)
 		:
 			Thread(env, "threaded_time_source", 8 * 1024 * sizeof(Genode::addr_t)),
+			_irq_dispatcher_component(*this),
 			_irq_dispatcher_cap(env.ep().rpc_ep().manage(&_irq_dispatcher_component))
 		{ }
 
diff --git a/repos/os/src/drivers/timer/nova/time_source.h b/repos/os/src/drivers/timer/nova/time_source.h
index ad7794bb4a..89d53a5770 100644
--- a/repos/os/src/drivers/timer/nova/time_source.h
+++ b/repos/os/src/drivers/timer/nova/time_source.h
@@ -28,22 +28,19 @@ class Timer::Time_source : public Threaded_time_source
 {
 	private:
 
-		Genode::addr_t           _sem = ~0UL;
-		unsigned long            _timeout_us = 0;
-		Genode::Trace::Timestamp _tsc_start = Genode::Trace::timestamp();
-		unsigned long            _tsc_khz;
+		Genode::addr_t           _sem        { ~0UL };
+		unsigned long            _timeout_us { 0 };
+		unsigned long            _tsc_khz    { 0 };
+		Duration                 _curr_time  { Microseconds(0) };
+		Genode::Trace::Timestamp _tsc_start  { Genode::Trace::timestamp() };
+		Genode::Trace::Timestamp _tsc_last   { _tsc_start };
 
 		/* 1 / ((us / (1000 * 1000)) * (tsc_khz * 1000)) */
 		enum { TSC_FACTOR = 1000ULL };
 
-		inline Microseconds _tsc_to_us(unsigned long long tsc,
-		                               bool sub_tsc_start = true) const
+		inline Genode::uint64_t _tsc_to_us(Genode::uint64_t tsc) const
 		{
-			if (sub_tsc_start) {
-				return Microseconds((tsc - _tsc_start) /
-				                    (_tsc_khz / TSC_FACTOR));
-			}
-			return Microseconds((tsc) / (_tsc_khz / TSC_FACTOR));
+			return (tsc) / (_tsc_khz / TSC_FACTOR);
 		}
 
 
@@ -62,10 +59,30 @@ class Timer::Time_source : public Threaded_time_source
 		 ** Genode::Time_source **
 		 *************************/
 
-		Microseconds max_timeout() const override { return _tsc_to_us(~0UL); }
-		void schedule_timeout(Microseconds duration, Timeout_handler &handler) override;
-		Duration curr_time() override {
-			return Duration(_tsc_to_us(Genode::Trace::timestamp())); }
+		void schedule_timeout(Microseconds duration,
+		                      Timeout_handler &handler) override;
+
+		Microseconds max_timeout() const override
+		{
+			unsigned long long const max_us_ull = _tsc_to_us(~0ULL);
+			return max_us_ull > ~0UL ? Microseconds(~0UL) : Microseconds(max_us_ull);
+		}
+
+		Duration curr_time() override
+		{
+			using namespace Genode::Trace;
+
+			Timestamp    const curr_tsc = timestamp();
+			Microseconds const diff(_tsc_to_us(curr_tsc - _tsc_last));
+
+			/* update in irq context or if update rate is below 4000 irq/s */
+			if (_irq || diff.value > 250) {
+				_curr_time += diff;
+				_tsc_last   = curr_tsc;
+			}
+
+			return _curr_time;
+		}
 };
 
 #endif /* _TIME_SOURCE_H_ */