<PAGE>
SAFECO COMMON STOCK TRUST
SAFECO TAX-EXEMPT BOND TRUST
SAFECO TAXABLE BOND TRUST
SAFECO MANAGED BOND TRUST
SAFECO MONEY MARKET TRUST
SUPPLEMENT TO THE ADVISOR CLASS STATEMENT OF ADDITIONAL
INFORMATION DATED APRIL 30, 1999
SUPPLEMENT DATED SEPTEMBER 1, 1999
THE FOLLOWING INFORMATION SUPPLEMENTS THE FOURTH PARAGRAPH FOLLOWING THE CAPTION
"DISTRIBUTION ARRANGEMENTS" ON PAGE 95-96 OF THE ADVISOR CLASS STATEMENT OF
ADDITIONAL INFORMATION:
In addition to the commissions and concessions described in the prospectus,
SAFECO Securities may, at its expense, pay additional commissions or
promotional incentives to dealers that sell shares of the Funds. Such
additional commissions or incentives may be offered only to dealers which
satisfy certain sales volume/growth criteria, or which meet other criteria
SAFECO Securities establishes from time to time. In connection with such a
marketing relationship, SAFECO Securities has agreed to pay WM Financial
Services, Inc. additional compensation in the amount of .25% on new sales,
other than sales of those Class A Shares which are sold at net asset value
and shares of the Money Market Fund for which .10% in additional
compensation will be paid.