diff --git a/etc/vicinage.api.md b/etc/vicinage.api.md
index ce71f2e..407c74e 100644
--- a/etc/vicinage.api.md
+++ b/etc/vicinage.api.md
@@ -161,7 +161,7 @@ export type ~PseudoElementKey = Extract<Pseudos, `::${string}`> | Extract<keyof
 export type ~PseudoElementRecord = Partial<Record<Exclude<~PseudoElementKey, Exclude<~ParameterizedPseudoElementKey, '::cue'>> | `${~ParameterizedPseudoElementKey}(${string})`, ~CommonProperties | ~CustomProperties | ~CompiledProperties>>;
 
 // @internal (undocumented)
-export type ~ResolvableValue<T> = null | T | (() => T) | readonly T[];
+export type ~ResolvableValue<T> = T | readonly T[] | (() => T | null | undefined) | null | undefined;
 
 // @internal (undocumented)
 export type ~SourceValue<T> = false | ~ResolvableValue<T> | ~ContextualValue<T>;
diff --git a/package.json b/package.json
index 235139c..23cf545 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "vicinage",
-  "version": "0.7.20",
+  "version": "0.7.21",
   "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 84a0d3c..43aad09 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -208,7 +208,12 @@ type SourceValue<T> = false | ResolvableValue<T> | ContextualValue<T>
 /**
  * @internal
  */
-type ResolvableValue<T> = null | T | (() => T) | readonly T[]
+type ResolvableValue<T> =
+  | T
+  | readonly T[]
+  | (() => T | null | undefined)
+  | null
+  | undefined
 
 /**
  * @internal