diff --git a/histories/models.py b/histories/models.py
index a0a8af7..7bcf5b2 100644
--- a/histories/models.py
+++ b/histories/models.py
@@ -68,18 +68,19 @@ def generate_partial_history(user, t_start):
     """ Generate the part of the history resulting from the crawl starting at
     the given url.
     """
+    timestamp = t_start
     result = []
     basis = generate_first_url(user)
-    result.append((basis, t_start))
-    t_start += 5* random.weibullvariate(1, 1.5)
+    result.append((basis, timestamp))
+    timestamp += 5* random.weibullvariate(1, 1.5)
     queue = Queue()
     crawler = crawl.CrawlingThread(user, basis, queue)
     crawler.start()
     crawler.join()
     urls = queue.get()
     for url in urls:
-        t_start += 5* random.weibullvariate(1, 1.5)
-        result.append((url, t_start)
+        timestamp += 5* random.weibullvariate(1, 1.5)
+        result.append((url, timestamp))
     return result
 
 def generate_first_url(user):