diff --git a/myhdl/Simulation.py b/myhdl/Simulation.py
index 14639c5e..6a022c13 100644
--- a/myhdl/Simulation.py
+++ b/myhdl/Simulation.py
@@ -196,6 +196,8 @@ class Simulation(object):
             except SuspendSimulation:
                 if not quiet:
                     printExcInfo()
+                if tracing:
+                    tracefile.flush()
                 return 1
 
             except StopSimulation:
diff --git a/myhdl/test_trace_sigs.py b/myhdl/test_trace_sigs.py
index 886909df..4db6d45f 100644
--- a/myhdl/test_trace_sigs.py
+++ b/myhdl/test_trace_sigs.py
@@ -34,8 +34,9 @@ path = os.path
 
 import unittest
 from unittest import TestCase
+import shutil
 
-from myhdl import delay, Signal
+from myhdl import delay, Signal, Simulation
 from trace_sigs import trace_sigs, TopLevelNameError, ArgTypeError, \
                        NoInstancesError
 
@@ -66,10 +67,20 @@ def top():
 
 class TestTraceSigs(TestCase):
 
+    def setUp(self):
+        self.paths = paths = ["dut.vcd", "inst.vcd"]
+        for p in paths:
+            if path.exists(p):
+                os.remove(p)
+
+    def tearDown(self):
+        for p in self.paths:
+            if path.exists(p):
+                os.remove(p)
+        
+
     def testTopName(self):
         p = "dut.vcd"
-        if path.exists(p):
-            os.remove(p)
         dut = trace_sigs(fun)
         try:
             trace_sigs(fun)
@@ -80,8 +91,6 @@ class TestTraceSigs(TestCase):
 
     def testArgType1(self):
         p = "dut.vcd"
-        if path.exists(p):
-            os.remove(p)
         try:
             dut = trace_sigs([1, 2])
         except ArgTypeError:
@@ -91,8 +100,6 @@ class TestTraceSigs(TestCase):
             
     def testArgType2(self):
         p = "dut.vcd"
-        if path.exists(p):
-            os.remove(p)
         try:
             dut = trace_sigs(gen, Signal(0))
         except ArgTypeError:
@@ -102,37 +109,39 @@ class TestTraceSigs(TestCase):
 
     def testReturnVal(self):
         p = "dut.vcd"
-        if path.exists(p):
-            os.remove(p)
         try:
             dut = trace_sigs(dummy)
         except NoInstancesError:
             pass
         else:
             self.fail()
+            
 
     def testHierarchicalTrace1(self):
         p = "inst.vcd"
-        if path.exists(p):
-            os.remove(p)
         top()
         self.assert_(path.exists(p))
         
     def testHierarchicalTrace2(self):
         pdut = "dut.vcd"
         psub = "inst.vcd"
-        for p in (pdut, psub):
-            if path.exists(p):
-                os.remove(p)
         dut = trace_sigs(top)
         self.assert_(path.exists(pdut))
         self.assert_(not path.exists(psub))
 
-    
-        
-        
+    def testBackupOutputFile(self):
+        p = "dut.vcd"
+        dut = trace_sigs(fun)
+        Simulation(dut).run(1000)
+        size = path.getsize(p)
+        pbak = p + '.' + str(path.getmtime(p))
+        self.assert_(not path.exists(pbak))
+        dut = trace_sigs(fun)
+        self.assert_(path.exists(p))
+        self.assert_(path.exists(pbak))
+        self.assert_(path.getsize(pbak) == size)
+        self.assert_(path.getsize(p) < size)
+        os.remove(pbak)
        
-       
-
 if __name__ == "__main__":
     unittest.main()
diff --git a/myhdl/trace_sigs.py b/myhdl/trace_sigs.py
index 7a2a568c..0facbf97 100644
--- a/myhdl/trace_sigs.py
+++ b/myhdl/trace_sigs.py
@@ -34,6 +34,9 @@ import re
 import string
 import time
 from types import FunctionType
+import os
+path = os.path
+import shutil
 
 from myhdl import _simulator, Signal, __version__
 from myhdl.util import _isGenSeq, _isgeneratorfunction
@@ -80,8 +83,12 @@ def trace_sigs(dut, *args, **kwargs):
         else:
             raise TopLevelNameError
         h = HierExtr(name, dut, *args, **kwargs)
-        vcdfilename = name + ".vcd"
-        vcdfile = open(vcdfilename, 'w')
+        vcdpath = name + ".vcd"
+        if path.exists(vcdpath):
+            backup = vcdpath + '.' + str(path.getmtime(vcdpath))
+            shutil.copyfile(vcdpath, backup)
+            os.remove(vcdpath)
+        vcdfile = open(vcdpath, 'w')
         _simulator._tracing = 1
         _simulator._tf = vcdfile
         _writeVcdHeader(vcdfile)