diff --git a/Grid/serialisation/JSON_IO.cc b/Grid/serialisation/JSON_IO.cc
index e47a2969..c92203ba 100644
--- a/Grid/serialisation/JSON_IO.cc
+++ b/Grid/serialisation/JSON_IO.cc
@@ -82,7 +82,7 @@ void JSONWriter::writeDefault(const std::string &s,	const std::string &x)
   if (s.size())
     ss_ << "\""<< s << "\" : \"" << os.str() << "\" ," ;
   else
-    ss_ << os.str() << " ," ;
+    ss_ << "\""<< os.str() << "\" ," ;
 }
 
 // Reader implementation ///////////////////////////////////////////////////////