diff --git a/.gitignore b/.gitignore
index bdd8e215..bb96b4ad 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,7 +1,8 @@
 .DS_Store
+.idea/
 npm-debug.log
 node_modules
 *.js
 *.map
 dist/
-dist_tests/
\ No newline at end of file
+dist_tests/
diff --git a/.npmignore b/.npmignore
index 1f03aff1..5fdd0760 100644
--- a/.npmignore
+++ b/.npmignore
@@ -1,4 +1,5 @@
 .DS_Store
+.idea
 .vscode
 npm-debug.log
 node_modules
diff --git a/README.md b/README.md
index e4ab0b2b..bcecfc08 100644
--- a/README.md
+++ b/README.md
@@ -89,6 +89,7 @@ See [server demo](example) and [browser demo](https://github.com/bcherny/json-sc
 | enableConstEnums | boolean | `true` | Prepend enums with [`const`](https://www.typescriptlang.org/docs/handbook/enums.html#computed-and-constant-members)? |
 | style | object | `{ bracketSpacing: false,  printWidth: 120,  semi: true,  singleQuote: false,  tabWidth: 2,  trailingComma: 'none',  useTabs: false }` | A [Prettier](https://prettier.io/docs/en/options.html) configuration |
 | unreachableDefinitions | boolean | `false` | Generates code for `definitions` that aren't referenced by the schema. |
+| strictIndexSignatures | boolean | `false` | Append all index signatures with `| undefined` so that they are strictly typed. |
 | $refOptions | object | `{}` | [$RefParser](https://github.com/BigstickCarpet/json-schema-ref-parser) Options, used when resolving `$ref`s |
 ## CLI
 
diff --git a/src/generator.ts b/src/generator.ts
index 9217871b..9b9d3f1e 100644
--- a/src/generator.ts
+++ b/src/generator.ts
@@ -145,6 +145,16 @@ function declareNamedTypes(
 }
 
 function generateType(ast: AST, options: Options): string {
+  const type = generateRawType(ast, options)
+
+  if (options.strictIndexSignatures && ast.keyName === '[k: string]') {
+    return `${type} | undefined`
+  }
+
+  return type
+}
+
+function generateRawType(ast: AST, options: Options): string {
   log(whiteBright.bgMagenta('generator'), ast)
 
   if (hasStandaloneName(ast)) {
diff --git a/src/index.ts b/src/index.ts
index 0f55176f..aefa0dbb 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -32,6 +32,12 @@ export interface Options {
    * Prepend enums with [`const`](https://www.typescriptlang.org/docs/handbook/enums.html#computed-and-constant-members)?
    */
   enableConstEnums: boolean
+  /**
+   * Append all index signatures with `| undefined` so that they are strictly typed.
+   *
+   * This is required to be compatible with `strictNullChecks`.
+   */
+  strictIndexSignatures: boolean
   /**
    * A [Prettier](https://prettier.io/docs/en/options.html) configuration.
    */
@@ -57,6 +63,7 @@ export const DEFAULT_OPTIONS: Options = {
   cwd: process.cwd(),
   declareExternallyReferenced: true,
   enableConstEnums: true, // by default, avoid generating code
+  strictIndexSignatures: false,
   style: {
     bracketSpacing: false,
     printWidth: 120,
diff --git a/test/__snapshots__/test/test.ts.md b/test/__snapshots__/test/test.ts.md
index 407ecf16..129ea76a 100644
--- a/test/__snapshots__/test/test.ts.md
+++ b/test/__snapshots__/test/test.ts.md
@@ -9425,3 +9425,20 @@ Generated by [AVA](https://ava.li).
       [k: string]: any;␊
     }␊
     `
+
+## strictIndexSignatures.js
+
+> Snapshot 1
+
+    `/* tslint:disable */␊
+    /**␊
+     * This file was automatically generated by json-schema-to-typescript.␊
+     * DO NOT MODIFY IT BY HAND. Instead, modify the source JSONSchema file,␊
+     * and run json-schema-to-typescript to regenerate this file.␊
+     */␊
+    ␊
+    export interface StrictIndexSignatures {␊
+      maybe?: string;␊
+      [k: string]: string | undefined;␊
+    }␊
+    `
diff --git a/test/__snapshots__/test/test.ts.snap b/test/__snapshots__/test/test.ts.snap
index e2744647..ab1bf00c 100644
Binary files a/test/__snapshots__/test/test.ts.snap and b/test/__snapshots__/test/test.ts.snap differ
diff --git a/test/e2e/strictIndexSignatures.ts b/test/e2e/strictIndexSignatures.ts
new file mode 100644
index 00000000..0b7f0e16
--- /dev/null
+++ b/test/e2e/strictIndexSignatures.ts
@@ -0,0 +1,16 @@
+export const input = {
+  title: 'StrictIndexSignatures',
+  type: 'object',
+  properties: {
+    maybe: {
+      type: 'string'
+    }
+  },
+  additionalProperties: {
+    type: 'string'
+  }
+}
+
+export const options = {
+  strictIndexSignatures: true
+}