diff --git a/ess/TraceWin.py b/ess/TraceWin.py
index 9ff5895f12dd14f76b7335a3cac7fc437febded9..103392fafdad89755a0b2ba560ccfad485e35732 100644
--- a/ess/TraceWin.py
+++ b/ess/TraceWin.py
@@ -720,6 +720,7 @@ class density_file:
                 if unit:
                     data_set.attrs['unit']=unit
 
+        fout.close()
 
 
 class remote_data_merger: