diff --git a/ddtrace/span.py b/ddtrace/span.py
index 97ab6c720e7..105ca804688 100644
--- a/ddtrace/span.py
+++ b/ddtrace/span.py
@@ -69,15 +69,25 @@ def __init__(self,
         self._tracer = tracer
         self._parent = None
 
+        # state
+        self._finished = False
+
     def finish(self, finish_time=None):
         """ Mark the end time of the span and submit it to the tracer.
+            If the span has already been finished don't do anything
 
             :param int finish_time: the end time of the span in seconds.
                                     Defaults to now.
         """
-        ft = finish_time or time.time()
-        # be defensive so we don't die if start isn't set
-        self.duration = ft - (self.start or ft)
+        if self._finished:
+            return
+        self._finished = True
+
+        if self.duration is None:
+            ft = finish_time or time.time()
+            # be defensive so we don't die if start isn't set
+            self.duration = ft - (self.start or ft)
+
         if self._tracer:
             self._tracer.record(self)
 
diff --git a/tests/test_span.py b/tests/test_span.py
index 9322f3f177b..c4e36beb74d 100644
--- a/tests/test_span.py
+++ b/tests/test_span.py
@@ -57,6 +57,26 @@ def test_finish():
     s2 = Span(tracer=None, name="foo")
     s2.finish()
 
+def test_finish_called_multiple_times():
+    # we should only record a span the first time finish is called on it
+    dt = DummyTracer()
+    assert dt.spans_recorded == 0
+    s = Span(dt, 'bar')
+    s.finish()
+    s.finish()
+    assert dt.spans_recorded == 1
+
+
+def test_finish_set_span_duration():
+    # If set the duration on a span, the span should be recorded with this
+    # duration
+    dt = DummyTracer()
+    assert dt.last_span is None
+    s = Span(dt, 'foo')
+    s.duration = 1337.0
+    s.finish()
+    assert dt.last_span.duration == 1337.0
+
 def test_traceback_with_error():
     s = Span(None, "foo")
     try:
@@ -121,7 +141,8 @@ class DummyTracer(object):
 
     def __init__(self):
         self.last_span = None
+        self.spans_recorded = 0
 
     def record(self, span):
         self.last_span = span
-
+        self.spans_recorded += 1