Bug description

This works (copied from an example in the docs)

import 'dotenv/config'
import { defineConfig, env } from "prisma/config";

type Env = {
  DATABASE_URL: string
}

export default defineConfig({
  schema: 'prisma/schema.prisma',
  migrations: {
    path: 'prisma/migrations',
  },
  datasource: {
    url: env<Env>('DATABASE_URL'),
  },
});

This, however, does not work
Notice how I changed from type to interface for Env

import 'dotenv/config'
import { defineConfig, env } from "prisma/config";

interface Env {
  DATABASE_URL: string
}

export default defineConfig({
  schema: 'prisma/schema.prisma',
  migrations: {
    path: 'prisma/migrations',
  },
  datasource: {
    url: env<Env>('DATABASE_URL'),
  },
});

The code above gives the following error

Type 'Env' does not satisfy the constraint 'Record<string, string | undefined>'.
Index signature for type 'string' is missing in type 'Env'. (ts 2344)

I think the generic for env should be updated to also allow using an interface like the one in the example above

Severity

🔹 Minor: Unexpected behavior, but does not block development

Reproduction

1. Follow your own docs here: https://www.prisma.io/docs/orm/reference/prisma-config-reference#type-safe-environment-variables
2. Change Env from being a type to being an interface instead.

Expected vs. Actual Behavior

Expected:

No TS errors

Actual:

Type 'Env' does not satisfy the constraint 'Record<string, string | undefined>'.
Index signature for type 'string' is missing in type 'Env'. (ts 2344)

Frequency

Consistently reproducible

Does this occur in development or production?

Only in development (e.g., CLI tools, migrations, Prisma Studio)

Is this a regression?

No, this is new functionality

Workaround

Add an index signature to the interface, like this:

interface Env {
  [key: string]: string | undefined
  DATABASE_URL: undefined
}

Prisma Schema & Queries

N/A

Prisma Config

import { defineConfig, env } from 'prisma/config'

interface Env {
  DATABASE_URL: undefined
}

const url = env<Env>('DATABASE_URL')

export default defineConfig({
  schema: 'db/schema.prisma',
  migrations: {
    path: 'db/migrations',
  },
  datasource: {
    url,
  },
})

Logs & Debug Info

N/A

Environment & Setup

• OS: macOS
• Database: Prisma Postgres
• Node.js version: v24.11.1

Prisma Version

❯ npx prisma -v
prisma                  : 6.19.0
@prisma/client          : 6.19.0
Computed binaryTarget   : darwin-arm64
Operating System        : darwin
Architecture            : arm64
Node.js                 : v24.11.1
TypeScript              : 5.9.2
Query Engine (Node-API) : libquery-engine 2ba551f319ab1df4bc874a89965d8b3641056773 (at node_modules/@prisma/engines/libquery_engine-darwin-arm64.dylib.node)
PSL                     : @prisma/prisma-schema-wasm 6.19.0-26.2ba551f319ab1df4bc874a89965d8b3641056773
Schema Engine           : schema-engine-cli 2ba551f319ab1df4bc874a89965d8b3641056773 (at node_modules/@prisma/engines/schema-engine-darwin-arm64)
Default Engines Hash    : 2ba551f319ab1df4bc874a89965d8b3641056773
Studio                  : 0.511.0