diff --git a/common/python/nomadcore/match_highlighter.py b/common/python/nomadcore/match_highlighter.py
index 31d85e882bb672d809ecc87eaf3b6f061e57212a..fdcf0b62121db0a50c135d5c69246b94c139b654 100644
--- a/common/python/nomadcore/match_highlighter.py
+++ b/common/python/nomadcore/match_highlighter.py
@@ -39,8 +39,9 @@ class MatchHighlighter(object):
             s,e=match.span(groupi)
             # logger.error("i:%d %3d %3d '%s'" % (groupi, s, e,
             #    match.group(groupi)))
-            ansiSwitch.append([s,1,ANSI.FG_RED])
-            ansiSwitch.append([e,0,ANSI.RESET_COLOR])
+            if match.group(groupi) is not None:
+                ansiSwitch.append([s,1,ANSI.FG_RED])
+                ansiSwitch.append([e,0,ANSI.RESET_COLOR])
         # sort by position, then by event
         ansiSwitch=sorted(ansiSwitch, key=itemgetter(0,1))
         if ansiSwitch[-1][0]>len(lineOrig):