diff --git a/pycbc/events/events.py b/pycbc/events/events.py
index <HASH>..<HASH> 100644
--- a/pycbc/events/events.py
+++ b/pycbc/events/events.py
@@ -63,7 +63,7 @@ def fc_cluster_over_window_fast(times, values, window_length):
         The reduced list of indices of the SNR values
     """
     if window_length <= 0:
-        return times
+        return numpy.arange(len(times))
 
     from scipy.weave import inline
     indices = numpy.zeros(len(times), dtype=int)
Fix small bug in clustering when window length = 0