Keeping a close eye on both dogs at this first meeting is of the utmost important. If it look like both dogs are not getting along, or they start growling at each other, step in the middle to cause a distraction give them treats. Keeping a calm voice, remind your older dog that this puppy is not threat to him. Keep intercept till the two dogs start showing a comfort zone. This should not take very long, they are simply deciding who the leader is and soon they should become friends. If there is extensive growling and/or persisting fighting between them, it would be better to stop and try again later, especially if aggression seems to be the problem.