Const enums (like the ones in <https://github.com/brianc/node-postgres/blob/master/packages/pg-protocol/src/messages.ts>) are a feature specific to Typescript projects built with `tsc` compiler. Builds that do not use `tsc` and only compile explicitly imported files need the `--isolatedModules` flag enabled, which does not suppport `const enum`s Please replace `const enum`s with normal enums.