"unable to get local issuer certificate" when uploading to S3 after upgrading to 2.9.0 beta9

Not sure if this is related to all those SMTP reports, but I have encountered a problem with my (non-AWS) S3 series when uploading:

SSL_connect returned=1 errno=0 peeraddr= state=error: certificate verify failed (unable to get local issuer certificate)

I checked the certificate and it seems fine as I have been able to connect to the S3 bucket.