mmysql.c fails to compile

[cwfoo]

Compiling mmysql.c using mmysql's Makefile fails with this error:

mmysql.c: In function ‘dbresult_finalize’:
mmysql.c:79:28: error: lvalue required as left operand of assignment
     DBresult_val(dbresval) = NULL;
                            ^
mmysql.c:81:33: error: lvalue required as left operand of assignment
     DBresultindex_val(dbresval) = NULL;
                                 ^

This is the function in question:

mosml/src/dynlibs/mmysql/mmysql.c

Lines 73 to 83 in ee355b2

	void dbresult_finalize(value dbresval)
	{
	MYSQL_RES* dbres = DBresult_val(dbresval);
	MYSQL_ROW_OFFSET* index = DBresultindex_val(dbresval);
	if (dbres != NULL) {
	mysql_free_result(dbres);
	DBresult_val(dbresval) = NULL;
	stat_free((char*)index);
	DBresultindex_val(dbresval) = NULL;
	}
	}

mosml version: 2.10.1
libmysqlclient version: 5.7.21
Compiler: gcc 7.5.0 (Ubuntu 7.5.0-3ubuntu1~18.04)
OS: Ubuntu 18.04.2