Oracle - Update string to replace only the last character

Oracle - Update string to replace only the last character

I have the following string in an Oracle 9i database:
A,B,C,
I need to replace all instances of ',' when it is the last item in the
string. I have come up with the following statement but it deletes
everything in the field not just the comma. Any suggestions?
UPDATE table SET column = REPLACE(SUBSTR(column, -1, 1), ',', '');