diff --git a/tools/xenmon/xenmon.py b/tools/xenmon/xenmon.py
index 4ccdf2f8c3..a95f126a23 100644
--- a/tools/xenmon/xenmon.py
+++ b/tools/xenmon/xenmon.py
@@ -502,6 +502,7 @@ def writelog():
     shm = mmap.mmap(shmf.fileno(), QOS_DATA_SIZE)
 
     interval = 0
+    curr = last = time.time()
     outfiles = {}
     for dom in range(0, NDOMAINS):
         outfiles[dom] = Delayed("%s-dom%d.log" % (options.prefix, dom), 'w')
@@ -561,9 +562,10 @@ def writelog():
                                      h1[dom][4], 
                                      h1[dom][5][0], h1[dom][5][1]))
                     outfiles[dom].flush()
-
-        interval += options.interval
-        time.sleep(1)
+            curr = time.time()
+            interval += (curr - last) * 1000
+            last = curr
+        time.sleep(options.interval / 1000.0)
 
     for dom in range(0, NDOMAINS):
         outfiles[dom].close()