diff --git a/reading_machine/src/Action.cpp b/reading_machine/src/Action.cpp
index 433adad653f54c6b55e4be2d850c3570688a105a..2d0aa648779929933f0461a0159c0dc84f879f4d 100644
--- a/reading_machine/src/Action.cpp
+++ b/reading_machine/src/Action.cpp
@@ -386,7 +386,7 @@ Action Action::addCurCharToCurWord()
 
   auto appliable = [](const Config & config, const Action &)
   {
-    return config.hasCharacter(config.getCharacterIndex()) and !util::isSeparator(config.getLetter(config.getCharacterIndex()));
+    return config.hasCharacter(config.getCharacterIndex()) and !util::isIllegal(config.getLetter(config.getCharacterIndex()));
   };
 
   return {Type::Write, apply, undo, appliable};