diff --git a/packages/csv-generate/dist/cjs/index.d.cts b/packages/csv-generate/dist/cjs/index.d.cts
index 581ed32f4..8e0931a87 100644
--- a/packages/csv-generate/dist/cjs/index.d.cts
+++ b/packages/csv-generate/dist/cjs/index.d.cts
@@ -5,6 +5,7 @@ import * as stream from "stream";
 type Callback = (err?: Error, records?: unknown) => void;
 
 export class Generator extends stream.Readable {
+  end(): void;
   constructor(options?: Options);
 
   readonly options: Options;
@@ -14,7 +15,9 @@ export type ColumnsFunctionArgs = {
   options: Options;
   state: State;
 };
-export type ColumnsFunction = (args: ColumnsFunctionArgs) => string;
+export type ColumnsFunction = (
+  args: ColumnsFunctionArgs,
+) => string | number | null;
 
 export type State = {
   start_time: number;
diff --git a/packages/csv-generate/dist/esm/index.d.ts b/packages/csv-generate/dist/esm/index.d.ts
index 581ed32f4..8e0931a87 100644
--- a/packages/csv-generate/dist/esm/index.d.ts
+++ b/packages/csv-generate/dist/esm/index.d.ts
@@ -5,6 +5,7 @@ import * as stream from "stream";
 type Callback = (err?: Error, records?: unknown) => void;
 
 export class Generator extends stream.Readable {
+  end(): void;
   constructor(options?: Options);
 
   readonly options: Options;
@@ -14,7 +15,9 @@ export type ColumnsFunctionArgs = {
   options: Options;
   state: State;
 };
-export type ColumnsFunction = (args: ColumnsFunctionArgs) => string;
+export type ColumnsFunction = (
+  args: ColumnsFunctionArgs,
+) => string | number | null;
 
 export type State = {
   start_time: number;
diff --git a/packages/csv-generate/lib/index.d.ts b/packages/csv-generate/lib/index.d.ts
index 581ed32f4..8e0931a87 100644
--- a/packages/csv-generate/lib/index.d.ts
+++ b/packages/csv-generate/lib/index.d.ts
@@ -5,6 +5,7 @@ import * as stream from "stream";
 type Callback = (err?: Error, records?: unknown) => void;
 
 export class Generator extends stream.Readable {
+  end(): void;
   constructor(options?: Options);
 
   readonly options: Options;
@@ -14,7 +15,9 @@ export type ColumnsFunctionArgs = {
   options: Options;
   state: State;
 };
-export type ColumnsFunction = (args: ColumnsFunctionArgs) => string;
+export type ColumnsFunction = (
+  args: ColumnsFunctionArgs,
+) => string | number | null;
 
 export type State = {
   start_time: number;
diff --git a/packages/csv-generate/test/options.columns.js b/packages/csv-generate/test/options.columns.ts
similarity index 93%
rename from packages/csv-generate/test/options.columns.js
rename to packages/csv-generate/test/options.columns.ts
index ab49d9aa4..1b00d7e26 100644
--- a/packages/csv-generate/test/options.columns.js
+++ b/packages/csv-generate/test/options.columns.ts
@@ -5,7 +5,7 @@ describe("Option `columns`", function () {
   it("as number", function (next) {
     this.timeout(1000000);
     let count = 0;
-    const data = [];
+    const data: Buffer[] = [];
     const generator = generate({ columns: 3 });
     generator.on("readable", () => {
       let d;
@@ -26,7 +26,7 @@ describe("Option `columns`", function () {
   it("as types", function (next) {
     this.timeout(1000000);
     let count = 0;
-    const data = [];
+    const data: Buffer[] = [];
     const generator = generate({ columns: ["int", "bool"], seed: 1 });
     generator.on("readable", () => {
       let d;
@@ -52,7 +52,7 @@ describe("Option `columns`", function () {
     try {
       generate({ columns: ["int", "bool", "invalid"] });
     } catch (err) {
-      err.message.should.eql(
+      (err as Error).message.should.eql(
         'Invalid column type: got "invalid", default values are ["ascii","int","bool"]',
       );
     }
@@ -61,7 +61,7 @@ describe("Option `columns`", function () {
   describe("user function", function () {
     it("accept string or null or number", function (next) {
       this.timeout(1000000);
-      const data = [];
+      const data: string[] = [];
       const generator = generate({
         length: 1,
         columns: [() => "a", () => null, () => 1],
@@ -81,6 +81,7 @@ describe("Option `columns`", function () {
 
     it("validate return argument", function (next) {
       this.timeout(1000000);
+      // @ts-expect-error Exercise runtime rejection of unsupported return values.
       const generator = generate({
         objectMode: true,
         columns: [() => ({})],
@@ -104,7 +105,7 @@ describe("Option `columns`", function () {
 
     it("validate arguments in objectMode", function (next) {
       this.timeout(1000000);
-      const data = [];
+      const data: unknown[] = [];
       const generator = generate({
         objectMode: true,
         length: 1,