diff --git a/scripts/ztplot.py b/scripts/ztplot.py
index f24500248bdb4a3e85a095bc9c45c2946e2464e6..f5a30076c62e29da6548d26d5d9d8a19af6eec24 100755
--- a/scripts/ztplot.py
+++ b/scripts/ztplot.py
@@ -112,7 +112,7 @@ class ZTPlot(kp.Module):
         hits = hits.append_columns('multiplicity', np.ones(len(hits)))
 
         for dom in doms:
-            dom_hits = hits[hits.dom_id == dom]
+            dom_hits = hits[hits.dom_id == dom].sorted(by='time')
             mltps, m_ids = count_multiplicities(dom_hits.time)
             hits['multiplicity'][hits.dom_id == dom] = mltps