diff --git a/core/suggestion.js b/core/suggestion.js
index 086a9b9..2300a07 100644
--- a/core/suggestion.js
+++ b/core/suggestion.js
@@ -520,6 +520,10 @@ module.exports = {
       selector:
         'CallExpression[callee.property.name="toString"][callee.optional=false][arguments.length=0][optional=false]',
       message: 'Use String() instead.'
+    },
+    {
+      selector: '[returnType.type="TSTypeAnnotation"]>TSTypeAnnotation>TSVoidKeyword',
+      message: 'Use undefined for non-returning functions of unknown for callbacks'
     }
   ],
 
diff --git a/examples/typescript-lib/src/add.ts b/examples/typescript-lib/src/add.ts
index 2444b97..7ebc03f 100644
--- a/examples/typescript-lib/src/add.ts
+++ b/examples/typescript-lib/src/add.ts
@@ -18,7 +18,7 @@ export function addSync(x: number, y: number): number {
  * @param y The value to add to x.
  * @param cb The callback that will be called with the sum of x and y.
  */
-export function addAsync(x: number, y: number, cb: Callback<number>): void {
+export function addAsync(x: number, y: number, cb: Callback<number>): undefined {
   cb(null, x + y)
 }
 
diff --git a/examples/typescript-lib/src/substract.ts b/examples/typescript-lib/src/substract.ts
index 343334f..8b658b1 100644
--- a/examples/typescript-lib/src/substract.ts
+++ b/examples/typescript-lib/src/substract.ts
@@ -19,7 +19,7 @@ export function substractSync(x: number, y: number): number {
  * @param y The value to substract from x.
  * @param cb The callback that will be called with the difference between x and y.
  */
-export function substractAsync(x: number, y: number, cb: Callback<number>): void {
+export function substractAsync(x: number, y: number, cb: Callback<number>): undefined {
   addAsync(x, -y, (error, result) => {
     if (error) {
       cb(error)
diff --git a/examples/typescript-lib/src/types.ts b/examples/typescript-lib/src/types.ts
index 44321e2..40e4b41 100644
--- a/examples/typescript-lib/src/types.ts
+++ b/examples/typescript-lib/src/types.ts
@@ -1 +1 @@
-export type Callback<T> = (error: Error | null, sum?: T) => void
+export type Callback<T> = (error: Error | null, sum?: T) => unknown
diff --git a/examples/typescript-preact/src/components/ErrorHandler/index.tsx b/examples/typescript-preact/src/components/ErrorHandler/index.tsx
index 41a62e8..3781093 100644
--- a/examples/typescript-preact/src/components/ErrorHandler/index.tsx
+++ b/examples/typescript-preact/src/components/ErrorHandler/index.tsx
@@ -29,7 +29,7 @@ export class ErrorHandler extends Component<ErrorHandlerProps, State> {
    *
    * @param error The error that was thrown
    */
-  componentDidCatch(error: Error): void {
+  componentDidCatch(error: Error): undefined {
     this.setState({ error })
   }
 
diff --git a/examples/typescript-preact/src/components/ItemForm/index.tsx b/examples/typescript-preact/src/components/ItemForm/index.tsx
index 5ef88c4..8feda78 100644
--- a/examples/typescript-preact/src/components/ItemForm/index.tsx
+++ b/examples/typescript-preact/src/components/ItemForm/index.tsx
@@ -10,7 +10,7 @@ interface ItemFormProps {
   /**
    * Called when the form is submitted
    */
-  onSubmit: (item: Item) => void
+  onSubmit: (item: Item) => unknown
 }
 
 /**
diff --git a/examples/typescript-react/src/components/ErrorHandler/index.tsx b/examples/typescript-react/src/components/ErrorHandler/index.tsx
index d203be5..8195fa1 100644
--- a/examples/typescript-react/src/components/ErrorHandler/index.tsx
+++ b/examples/typescript-react/src/components/ErrorHandler/index.tsx
@@ -36,7 +36,7 @@ export class ErrorHandler extends Component<ErrorHandlerProps, State> {
    * @param error The error that was thrown
    * @param errorInfo The React error information
    */
-  componentDidCatch(error: Error, errorInfo: ErrorInfo): void {
+  componentDidCatch(error: Error, errorInfo: ErrorInfo): undefined {
     this.setState({ error, errorInfo })
   }
 
diff --git a/examples/typescript-react/src/components/ItemForm/index.tsx b/examples/typescript-react/src/components/ItemForm/index.tsx
index ee2b1d4..82746fd 100644
--- a/examples/typescript-react/src/components/ItemForm/index.tsx
+++ b/examples/typescript-react/src/components/ItemForm/index.tsx
@@ -9,7 +9,7 @@ interface ItemFormProps {
   /**
    * Called when the form is submitted
    */
-  onSubmit: (item: Item) => void
+  onSubmit: (item: Item) => unknown
 }
 
 /**