diff --git a/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java b/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
index 5f0a3220..50289ef7 100644
--- a/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
+++ b/opentracing-mock/src/main/java/io/opentracing/mock/MockSpan.java
@@ -1,5 +1,5 @@
 /**
- * Copyright 2016 The OpenTracing Authors
+ * Copyright 2016-2017 The OpenTracing Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
diff --git a/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java b/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java
index c83f9066..dbfa6249 100644
--- a/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java
+++ b/opentracing-mock/src/main/java/io/opentracing/mock/MockTracer.java
@@ -1,5 +1,5 @@
 /**
- * Copyright 2016 The OpenTracing Authors
+ * Copyright 2016-2017 The OpenTracing Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -173,6 +173,9 @@ public Tracer.SpanBuilder withStartTimestamp(long microseconds) {
 
         @Override
         public Span start() {
+            if (this.startMicros == 0) {
+                this.startMicros = MockSpan.nowMicros();
+            }
             return new MockSpan(MockTracer.this, this.operationName, this.startMicros, initialTags, this.firstParent);
         }
 
diff --git a/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java b/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java
index 178c0caf..ce6461ec 100644
--- a/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java
+++ b/opentracing-mock/src/test/java/io/opentracing/mock/MockTracerTest.java
@@ -1,5 +1,5 @@
 /**
- * Copyright 2016 The OpenTracing Authors
+ * Copyright 2016-2017 The OpenTracing Authors
  *
  * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
  * in compliance with the License. You may obtain a copy of the License at
@@ -13,15 +13,17 @@
  */
 package io.opentracing.mock;
 
-import io.opentracing.Span;
-import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
 
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 
-import static org.junit.Assert.assertEquals;
-import static org.junit.Assert.assertNotEquals;
+import org.junit.Assert;
+import org.junit.Test;
+
+import io.opentracing.Span;
 
 public class MockTracerTest {
     @Test
@@ -99,4 +101,38 @@ public void testChildSpan() {
         assertEquals(parent.context().spanId(), child.parentId());
         assertEquals(parent.context().traceId(), child.context().traceId());
     }
+
+    @Test
+    public void testStartTimestamp() throws InterruptedException {
+        MockTracer tracer = new MockTracer();
+        long startMicros;
+        {
+            MockTracer.SpanBuilder fooSpan = tracer.buildSpan("foo");
+            Thread.sleep(2);
+            startMicros = System.currentTimeMillis() * 1000;
+            fooSpan.start().finish();
+        }
+        List<MockSpan> finishedSpans = tracer.finishedSpans();
+
+        Assert.assertEquals(1, finishedSpans.size());
+        MockSpan span = finishedSpans.get(0);
+        Assert.assertTrue(startMicros <= span.startMicros());
+        Assert.assertTrue(System.currentTimeMillis() * 1000 >= span.finishMicros());
+    }
+
+    @Test
+    public void testStartExplicitTimestamp() throws InterruptedException {
+        MockTracer tracer = new MockTracer();
+        long startMicros = 2000;
+        {
+            tracer.buildSpan("foo")
+                    .withStartTimestamp(startMicros)
+                    .start()
+                    .finish();
+        }
+        List<MockSpan> finishedSpans = tracer.finishedSpans();
+
+        Assert.assertEquals(1, finishedSpans.size());
+        Assert.assertEquals(startMicros, finishedSpans.get(0).startMicros());
+    }
 }