diff --git a/src/Parser.cpp b/src/Parser.cpp
index 15b2d9d90..19a28a8f9 100644
--- a/src/Parser.cpp
+++ b/src/Parser.cpp
@@ -104,6 +104,8 @@ void Parser::initialize (int argc, const char** argv)
 
         if (l->second == Lexer::typeOperator)
           sub->tag ("OP");
+        else
+          sub->tag ("?");
 
         // TODO More types needed.  Perhaps.
       }