Start a v2.6 MongoDB instance and create an external user: ~/bin/mongodb/2.6.1-ent/mongod --dbpath ~/data/destroy/ --logpath ~/data/destroy/mongod.log --fork --setParameter authenticationMechanisms=GSSAPI,MONGODB-CR --smallfiles --noprealloc db.getSiblingDB('$external').createUser({user: "aks@WIN2012.AKS.EVILS.IN", roles: [{db: "admin", role: "root"}]}) db.getSiblingDB('admin').system.users.find() Restart a v3.0.3 MongoDB instance and perform authSchemaUpgrade ~/bin/mongodb/3.0.3-ent/mongod --dbpath ~/data/destroy/ --logpath ~/data/destroy/mongod.log --fork --setParameter authenticationMechanisms=GSSAPI,MONGODB-CR --smallfiles --noprealloc db.adminCommand({authSchemaUpgrade: 1}); This should result in the following error: { "ok" : 0, "errmsg" : "While preparing to upgrade user doc from 2.6/3.0 user data schema to the 3.0 SCRAM only schema, found a user doc missing MONGODB-CR credentials :{ _id: \"$external.aks@WIN2012.AKS.EVILS.IN\", user: \"aks@WIN2012.AKS.EVILS.IN\", db: \"$external\", credentials: { external: true }, roles: [ { role: \"root\", db: \"admin\" } ] }", "code" : 18744 }