diff --git a/src/App/Expression.cpp b/src/App/Expression.cpp
index 010a4a9840..b42bc9ba3e 100644
--- a/src/App/Expression.cpp
+++ b/src/App/Expression.cpp
@@ -1578,6 +1578,7 @@ void OperatorExpression::_toString(std::ostream &s, bool persistent,int) const
         s << " >= ";
         break;
     case UNIT:
+        s << " ";
         break;
     default:
         assert(0);