ORA-00922: missing or invalid option

We routinely change Oracle passwords as part of security best-practice, I keep hitting this and keep forgetting why! :-)

ALTER USER DAC_REPO IDENTIFIED BY 1KoBe3RH REPLACE YlR94tqp
Error report:
SQL Error: ORA-00922: missing or invalid option
00922. 00000 - "missing or invalid option"
*Cause:
*Action:

Someone better qualified than me can explain why but I suspect it's the leading number in the new password. Quoting the passwords then works fine:

ALTER USER DAC_REPO IDENTIFIED BY "1KoBe3RH" REPLACE "YlR94tqp"

ALTER USER DAC_REPO succeeded.