diff --git a/etc/vicinage.api.md b/etc/vicinage.api.md
index 9272bd1..df32bc5 100644
--- a/etc/vicinage.api.md
+++ b/etc/vicinage.api.md
@@ -22,7 +22,7 @@ export const apply: (...styledeck: StyleDeck[]) => ReturnType<typeof props>;
 export const sheet: <T extends StyleDeck[]>(...styledeck: T) => T;
 
 // @public (undocumented)
-export type StyleDeck<T extends ~PropertiesWithExtras = ~PropertiesWithExtras> = StyleDeck<T>[] | ~StyleCard<T> | readonly [~StyleCard<T>, InlineStyles] | Theme<VarGroup<{}>> | ~NonApplicableThemeProperties | ~NonApplicableObjectProperties | ~NonApplicableSymbolProperties;
+export type StyleDeck<T extends ~PropertiesWithExtras = ~PropertiesWithExtras> = StyleDeck<T>[] | ~StyleCard<T> | readonly [~StyleCard<T>, InlineStyles] | Theme<VarGroup<{}>> | ~NonApplicableThemeProperties | ~NonApplicableObjectProperties | ~NonApplicableSymbolProperties | undefined;
 
 // @internal (undocumented)
 export type ~CommonProperties = Properties & Omit<CSSPropertiesWithExtras, keyof Properties | `::${string}`>;
diff --git a/package.json b/package.json
index ba4a549..62cf0bd 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "vicinage",
-  "version": "0.6.19",
+  "version": "0.6.20",
   "description": "Type-safe and zero-runtime UI styling, right in the markup.",
   "license": "MIT",
   "repository": {
diff --git a/src/index.ts b/src/index.ts
index 090f164..78b8e35 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -35,6 +35,7 @@ type StyleDeck<T extends StyleConfig = StyleConfig> =
   | NonApplicableThemeProperties
   | NonApplicableObjectProperties
   | NonApplicableSymbolProperties
+  | undefined
 
 /**
  * Apply styles as props `{ className, style }`, or attrs `{ class, style }`.
diff --git a/src/styledeck.spec-d.tsx b/src/styledeck.spec-d.tsx
index ab949c8..8a21440 100644
--- a/src/styledeck.spec-d.tsx
+++ b/src/styledeck.spec-d.tsx
@@ -3,6 +3,11 @@ const tokens = defineVars({
 })
 
 describe('StyleDeck', () => {
+  it('accepts undefined', () => {
+    // eslint-disable-next-line unicorn/no-useless-undefined
+    assertType<StyleDeck>(undefined)
+  })
+
   it('accepts standard properties', () => {
     assertType<StyleDeck>({
       color: 'red',