AWS Route 53 CNAME with long destination URL not allowed

I'm adding a CNAME entry into Route 53. The URL I'm trying to redirect to (i.e. destination) has a large number of characters. When I try to add it I get this error:

Error occurred
Bad request.
(InvalidChangeBatch 400: DomainLabelTooLong (Domain label is too long) encountered with '<my-url>', Unparseable CNAME encountered)

After some fiddling it looks like it gives me this error if the URL is longer than 70 characters. If the URL has less than that, it works fine. I can't find anywhere documenting this limit, so is it a bug? Is there any way to increase this limit?

Here is the relevant information from the Route53 documentation:

Domain names (including the names of domains, hosted zones, and records) consist of a series of labels separated by dots. Each label can be up to 63 bytes long. The total length of a domain name cannot exceed 255 bytes, including the dots.

Wikipedia provides similar information:

A label may contain zero to 63 characters. The null label, of length zero, is reserved for the root zone. The full domain name may not exceed the length of 253 characters in its textual representation. In the internal binary representation of the DNS the maximum length requires 255 octets of storage, as it also stores the length of the name.