AWS Lambda Layer/Node: Postgres client fails with "self-signed certificate in certificate chain"

Question

I am working in AWS Lambda with a Postgres RDS, and I am trying to move my database management code into a Lambda Layer that can be shared across functions. The code works perfectly fine in the function, but when I move it to the layer it dies with the error:

Unhandled Promise Rejection     
{
   "errorType":"Runtime.UnhandledPromiseRejection",
   "errorMessage":"Error: self-signed certificate in certificate chain",
   ...
}

The gist of my Postgres client code is as follows:

const pg = require('pg')
# db_info is pulled from Secrets Manager
let client = new pg.Client({
            host: db_info.host,
            user: db_info.username,
            database: db_info.dbName,
            password: db_info.password,
            port: db_info.port,
            ssl: true
        });
        client.connect();

I am a newbie to AWS Lambda, so I'm somewhat flying blind. Any suggestions are greatly appreciated.