diff --git a/repos/base-nova/include/nova/syscall-generic.h b/repos/base-nova/include/nova/syscall-generic.h
index 75a7f8e179..2aa12d948d 100644
--- a/repos/base-nova/include/nova/syscall-generic.h
+++ b/repos/base-nova/include/nova/syscall-generic.h
@@ -756,6 +756,7 @@ namespace Nova {
 		PT_SEL_PARENT     = 0x1a,  /* convention on Genode */
 		PT_SEL_MAIN_EC    = 0x1c,  /* convention on Genode */
 		PT_SEL_STARTUP    = 0x1e,
+		SM_SEL_SIGNAL     = 0x1e,  /* alias of PT_SEL_STARTUP */
 		PT_SEL_RECALL     = 0x1f,
 		SM_SEL_EC         = 0x1d,  /* convention on Genode */
 	};
diff --git a/repos/base-nova/src/include/signal_source/client.h b/repos/base-nova/src/include/signal_source/client.h
index 83a2caf9d7..1ff928e52b 100644
--- a/repos/base-nova/src/include/signal_source/client.h
+++ b/repos/base-nova/src/include/signal_source/client.h
@@ -54,9 +54,10 @@ namespace Genode {
 			{
 				/* request mapping of semaphore capability selector */
 				Thread * myself = Thread::myself();
-				request_signal_sm_cap(myself->native_thread().exc_pt_sel + Nova::PT_SEL_PAGE_FAULT,
-				                      myself->native_thread().exc_pt_sel + Nova::PT_SEL_STARTUP);
-				_sem = Capability_space::import(myself->native_thread().exc_pt_sel + Nova::PT_SEL_STARTUP);
+				auto const &exc_base = myself->native_thread().exc_pt_sel;
+				request_signal_sm_cap(exc_base + Nova::PT_SEL_PAGE_FAULT,
+				                      exc_base + Nova::SM_SEL_SIGNAL);
+				_sem = Capability_space::import(exc_base + Nova::SM_SEL_SIGNAL);
 				call<Rpc_register_semaphore>(_sem);
 			}
 
diff --git a/repos/base-nova/src/timer/nova/time_source.cc b/repos/base-nova/src/timer/nova/time_source.cc
index ebf83fb4a5..d1b9fb697b 100644
--- a/repos/base-nova/src/timer/nova/time_source.cc
+++ b/repos/base-nova/src/timer/nova/time_source.cc
@@ -28,7 +28,7 @@ void Timer::Time_source::schedule_timeout(Microseconds     duration,
 	Threaded_time_source::handler(handler);
 
 	/* check whether to cancel last timeout */
-	if (duration.value == 0 && _sem != ~0UL) {
+	if (duration.value == 0 && _sem) {
 		uint8_t res = Nova::sm_ctrl(_sem, Nova::SEMAPHORE_UP);
 		if (res != Nova::NOVA_OK)
 			nova_die();
@@ -40,10 +40,14 @@ void Timer::Time_source::schedule_timeout(Microseconds     duration,
 
 void Timer::Time_source::_wait_for_irq()
 {
-	if (_sem == ~0UL) {
-		_sem = Thread::native_thread().exc_pt_sel + SM_SEL_EC; }
+	if (!_sem) {
+		/* initialize first time in context of running thread */
+		auto const &exc_base = Thread::native_thread().exc_pt_sel;
+		request_signal_sm_cap(exc_base + Nova::PT_SEL_PAGE_FAULT,
+		                      exc_base + Nova::SM_SEL_SIGNAL);
 
-	addr_t sem = _sem;
+		_sem = Thread::native_thread().exc_pt_sel + SM_SEL_SIGNAL;
+	}
 
 	/* calculate absolute timeout */
 	Trace::Timestamp now   = Trace::timestamp();
@@ -52,7 +56,7 @@ void Timer::Time_source::_wait_for_irq()
 	if (_timeout_us == max_timeout().value) {
 
 		/* tsc_absolute == 0 means blocking without timeout */
-		uint8_t res = sm_ctrl(sem, SEMAPHORE_DOWN, 0);
+		uint8_t res = sm_ctrl(_sem, SEMAPHORE_DOWN, 0);
 		if (res != Nova::NOVA_OK && res != Nova::NOVA_TIMEOUT) {
 			nova_die(); }
 
@@ -60,7 +64,7 @@ void Timer::Time_source::_wait_for_irq()
 
 		/* block until timeout fires or it gets canceled */
 		unsigned long long tsc_absolute = now + us_64 * (_tsc_khz / TSC_FACTOR);
-		uint8_t res = sm_ctrl(sem, SEMAPHORE_DOWN, tsc_absolute);
+		uint8_t res = sm_ctrl(_sem, SEMAPHORE_DOWN, tsc_absolute);
 		if (res != Nova::NOVA_OK && res != Nova::NOVA_TIMEOUT) {
 			nova_die(); }
 	}
diff --git a/repos/base-nova/src/timer/nova/time_source.h b/repos/base-nova/src/timer/nova/time_source.h
index fa3fe8beb4..7145d57a41 100644
--- a/repos/base-nova/src/timer/nova/time_source.h
+++ b/repos/base-nova/src/timer/nova/time_source.h
@@ -57,7 +57,7 @@ class Timer::Time_source : public Threaded_time_source
 			return 1000*1000;
 		}
 
-		Genode::addr_t           _sem        { ~0UL };
+		Genode::addr_t           _sem        { 0 };
 		uint64_t                 _timeout_us { 0 };
 		unsigned long      const _tsc_khz;
 		Duration                 _curr_time  { Microseconds(0) };