Hi Sven - This is in Pharo 6.1. There is an API I'm using which sometimes returns a string only containing a single instance of the number 0 in the "Expires" field, so the #expiresTimeStamp method sends that to #parseHttpDate: and since it can't be parsed into a date an error is thrown. Seems like Zinc should be able to handle that based on the spec here: https://tools.ietf.org/html/rfc7234#section-5.3 Would you rather I changed the implementation of parseHttpDate: to add an empty check on the parsed tokens e.g. parseHttpDate: string "self parseHttpDate: 'Tue, 13 Sep 2011 08:04:49 GMT'." "self parseHttpDate: 'Tue, 13-Sep-2011 08:04:51 GMT'." "self parseHttpDate: 'Tue Jan 01 00:00:01 2036 GMT'." | tokens day month year hour minute second months map yearToken | string size = 1 ifTrue:[ ^DateAndTime epoch ]. tokens := (string findTokens: #( $ $- $: $, )) allButFirst. ... Or add a string size guard check in #expiresTimeStamp ? e.g. expiresTimeStamp self expires ifNil: [ ^ DateAndTime now + 1 day ] ifNotNil: [ :exp | exp size = 1 ifTrue: [ ^ DateAndTime epoch ]. ^ ZnUtils parseHttpDate: exp ] Thanks Paul