Ubuntu Trusty repository broken; apt-get update fails

Ign http://apt.puppetlabs.com trusty InRelease                     

Hit http://apt.puppetlabs.com trusty Release.gpg   

Hit http://apt.puppetlabs.com trusty Release       

W: Failed to fetch http://apt.puppetlabs.com/dists/trusty/Release  Unable to find expected entry 'main/source/Sources' in Release file (Wrong sources.list entry or malformed file)

E: Some index files failed to download. They have been ignored, or old ones used instead.

$ cat /etc/apt/sources.list.d/puppetlabs.list 

# Puppetlabs products

deb http://apt.puppetlabs.com trusty main

deb-src http://apt.puppetlabs.com trusty main

# Puppetlabs dependencies

deb http://apt.puppetlabs.com trusty dependencies

deb-src http://apt.puppetlabs.com trusty dependencies

# Puppetlabs devel (uncomment to activate)

# deb http://apt.puppetlabs.com trusty devel

# deb-src http://apt.puppetlabs.com trusty devel