diff --git a/extensions/fablabchemnitz/contour_scanner_and_trimmer/contour_scanner_and_trimmer.py b/extensions/fablabchemnitz/contour_scanner_and_trimmer/contour_scanner_and_trimmer.py
index 8d317681..dd9ebe7c 100644
--- a/extensions/fablabchemnitz/contour_scanner_and_trimmer/contour_scanner_and_trimmer.py
+++ b/extensions/fablabchemnitz/contour_scanner_and_trimmer/contour_scanner_and_trimmer.py
@@ -695,7 +695,8 @@ class ContourScannerAndTrimmer(inkex.EffectExtension):
            so.highlight_merges is True:
             so.draw_subsplit = True
             
-        if so.highlight_merges is True:
+        if so.highlight_duplicates is True or \
+           so.highlight_merges is True:
             so.filter_subsplit_collinear = True
      
         if so.filter_subsplit_collinear is True: #this is a must.