diff --git a/base-pistachio/src/core/include/platform_thread.h b/base-pistachio/src/core/include/platform_thread.h
index d4b2daefd..ab67181a1 100644
--- a/base-pistachio/src/core/include/platform_thread.h
+++ b/base-pistachio/src/core/include/platform_thread.h
@@ -68,12 +68,11 @@ namespace Genode {
 			 *
 			 * \param ip      instruction pointer to start at
 			 * \param sp      stack pointer to use
-			 * \param cpu_no  target cpu
 			 *
 			 * \retval  0  successful
 			 * \retval -1  thread could not be started
 			 */
-			int start(void *ip, void *sp, unsigned int cpu_no = 0);
+			int start(void *ip, void *sp);
 
 			/**
 			 * Pause this thread
diff --git a/base-pistachio/src/core/platform_thread.cc b/base-pistachio/src/core/platform_thread.cc
index 2e489dd0f..ef31133ca 100644
--- a/base-pistachio/src/core/platform_thread.cc
+++ b/base-pistachio/src/core/platform_thread.cc
@@ -50,8 +50,9 @@ void Platform_thread::affinity(Affinity::Location location)
 		return;
 	}
 
-	if (L4_Set_ProcessorNo(_l4_thread_id, cpu_no) == 0)
-		PERR("Error setting processor number.");
+	if (_l4_thread_id != L4_nilthread)
+		if (L4_Set_ProcessorNo(_l4_thread_id, cpu_no) == 0)
+			PERR("Error setting processor number.");
 }
 
 
@@ -61,7 +62,7 @@ Affinity::Location Platform_thread::affinity()
 }
 
 
-int Platform_thread::start(void *ip, void *sp, unsigned int cpu_no)
+int Platform_thread::start(void *ip, void *sp)
 {
 	L4_ThreadId_t thread = _l4_thread_id;
 	L4_ThreadId_t pager  = _pager ? _pager->cap().dst() : L4_nilthread;
@@ -108,7 +109,7 @@ int Platform_thread::start(void *ip, void *sp, unsigned int cpu_no)
 	}
 
 	/* get the thread running on the right cpu */
-	affinity(Affinity::Location(cpu_no, 0));
+	affinity(_location);
 
 	/* assign priority */
 	if (!L4_Set_Priority(thread,
diff --git a/base/src/core/cpu_session_component.cc b/base/src/core/cpu_session_component.cc
index 6592eb167..436c3f139 100644
--- a/base/src/core/cpu_session_component.cc
+++ b/base/src/core/cpu_session_component.cc
@@ -53,6 +53,9 @@ Thread_capability Cpu_session_component::create_thread(Name  const &name,
 		                                                  _default_exception_handler,
 		                                                  trace_control_index,
 		                                                  *trace_control);
+
+		/* set default affinity defined by CPU session */
+		thread->platform_thread()->affinity(_location);
 	} catch (Allocator::Out_of_memory) {
 		throw Out_of_metadata();
 	}
@@ -122,13 +125,6 @@ int Cpu_session_component::start(Thread_capability thread_cap,
 	 */
 	thread->update_exception_sigh();
 
-	/*
-	 * If no affinity location was set for this specific thread before,
-	 * we set the one which was defined for the whole CPU session.
-	 */
-	if (!thread->platform_thread()->affinity().valid())
-		thread->platform_thread()->affinity(_location);
-
 	return thread->platform_thread()->start((void *)ip, (void *)sp);
 }