Finally fixed issue reported in #149
diff --git a/coders/json.c b/coders/json.c
index 4336230..4288d3b 100644
--- a/coders/json.c
+++ b/coders/json.c
@@ -1464,7 +1464,7 @@
                 case 219: tag="Custom Field 20"; break;
                 default: tag="unknown"; break;
               }
-              (void) FormatLocaleFile(file,"      %s[%.20g,%.20g]: ",tag,
+              (void) FormatLocaleFile(file,"      \"%s[%.20g,%.20g]\": ",tag,
                 (double) dataset,(double) record);
               length=(size_t) (GetStringInfoDatum(profile)[i++] << 8);
               length|=GetStringInfoDatum(profile)[i++];