diff --git a/vm/debug.cpp b/vm/debug.cpp
index 6787bdc725..178b9b9381 100755
--- a/vm/debug.cpp
+++ b/vm/debug.cpp
@@ -390,6 +390,9 @@ void factor_vm::factorbug()
 		exit(1);
 	}
 
+	if (sampling_profiler_p)
+		end_sampling_profiler();
+
 	fep_p = true;
 
 	std::cout << "Starting low level debugger..." << std::endl;
diff --git a/vm/os-windows.cpp b/vm/os-windows.cpp
index 389732ed9c..2ab696715c 100755
--- a/vm/os-windows.cpp
+++ b/vm/os-windows.cpp
@@ -312,7 +312,7 @@ void factor_vm::sampler_thread_loop()
 	assert(QueryPerformanceCounter(&counter));
 	while (FACTOR_MEMORY_BARRIER(), sampling_profiler_p)
 	{
-		Sleep(0);
+		SwitchToThread();
 		assert(QueryPerformanceCounter(&new_counter));
 		cell samples = 0;
 		while (new_counter.QuadPart - counter.QuadPart > units_per_sample) {
@@ -320,7 +320,8 @@ void factor_vm::sampler_thread_loop()
 			++samples;
 			counter.QuadPart += units_per_sample;
 		}
-		enqueue_safepoint_sample(samples, 0, false);
+		if (samples > 0)
+			enqueue_safepoint_sample(samples, 0, false);
 	}
 }
 
@@ -344,6 +345,8 @@ void factor_vm::start_sampling_profiler_timer()
 
 void factor_vm::end_sampling_profiler_timer()
 {
+	sampling_profiler_p = false;
+	FACTOR_MEMORY_BARRIER();
 	DWORD wait_result = WaitForSingleObject(sampler_thread,
 		3000/FACTOR_PROFILE_SAMPLES_PER_SECOND);
 	if (wait_result != WAIT_OBJECT_0)
diff --git a/vm/sampling_profiler.cpp b/vm/sampling_profiler.cpp
index cacc9ab6f9..9a7a4685b4 100644
--- a/vm/sampling_profiler.cpp
+++ b/vm/sampling_profiler.cpp
@@ -92,6 +92,8 @@ void factor_vm::start_sampling_profiler()
 {
 	safepoint_sample_count = 0;
 	safepoint_gc_sample_count = 0;
+	safepoint_foreign_sample_count = 0;
+	safepoint_foreign_thread_sample_count = 0;
 	clear_samples();
 	samples.reserve(10*FACTOR_PROFILE_SAMPLES_PER_SECOND);
 	sample_callstacks.reserve(100*FACTOR_PROFILE_SAMPLES_PER_SECOND);
diff --git a/vm/vm.cpp b/vm/vm.cpp
index 47669f615a..bdb5158a15 100755
--- a/vm/vm.cpp
+++ b/vm/vm.cpp
@@ -12,6 +12,8 @@ factor_vm::factor_vm() :
 	safepoint_fep(false),
 	safepoint_sample_count(0),
 	safepoint_gc_sample_count(0),
+	safepoint_foreign_sample_count(0),
+	safepoint_foreign_thread_sample_count(0),
 	gc_off(false),
 	current_gc(NULL),
 	gc_events(NULL),