diff --git a/src/kaiku.ts b/src/kaiku.ts
index c10c84a..22f9008 100644
--- a/src/kaiku.ts
+++ b/src/kaiku.ts
@@ -254,7 +254,12 @@ type Render = <PropertiesT extends DefaultProps>(
   rootElement: HTMLElement | SVGElement
 ) => void
 
-type ClassNames = undefined | null | string | { [key: string]: boolean } | ClassNames[]
+type ClassNames =
+  | undefined
+  | null
+  | string
+  | { [key: string]: boolean }
+  | ClassNames[]
 
 //
 //  Generic utilities
diff --git a/test/kaiku.spec.tsx b/test/kaiku.spec.tsx
index 884c5d8..1e1f3ef 100644
--- a/test/kaiku.spec.tsx
+++ b/test/kaiku.spec.tsx
@@ -1948,9 +1948,7 @@ describe('kaiku', () => {
 
   it('should handle array of classnames including `undefined`', async () => {
     const App = () => {
-      return (
-        <div class={[undefined]}/>
-      )
+      return <div class={[undefined]} />
     }
 
     render(<App />, rootNode)
@@ -1959,9 +1957,7 @@ describe('kaiku', () => {
 
   it('should handle array of classnames including `null`', async () => {
     const App = () => {
-      return (
-        <div class={[null]}/>
-      )
+      return <div class={[null]} />
     }
 
     render(<App />, rootNode)