*** a/src/backend/utils/adt/jsonfuncs.c
--- b/src/backend/utils/adt/jsonfuncs.c
*************** populate_record_worker(FunctionCallInfo
*** 2160,2165 ****
--- 2160,2167 ----
  		my_extra = (RecordIOData *) fcinfo->flinfo->fn_extra;
  		my_extra->record_type = InvalidOid;
  		my_extra->record_typmod = 0;
+ 		my_extra->ncolumns = ncolumns;
+ 		MemSet(my_extra->columns, 0, sizeof(ColumnIOData) * ncolumns);
  	}
  
  	if (have_record_arg && (my_extra->record_type != tupType ||