diff --git a/clients/web/src/test/core/nullableUnion.test.ts b/clients/web/src/test/core/nullableUnion.test.ts
index c1054c83..24592e24 100644
--- a/clients/web/src/test/core/nullableUnion.test.ts
+++ b/clients/web/src/test/core/nullableUnion.test.ts
@@ -768,6 +768,12 @@ describe("admitsNull", () => {
       );
     });
 
+    it("reads the boolean schema form", () => {
+      // `true` is the unconstrained schema; `false` admits nothing at all.
+      expect(admitsNull({ const: null, anyOf: [true] })).toBe(true);
+      expect(admitsNull({ const: null, anyOf: [false] })).toBe(false);
+    });
+
     it("does not override a sibling that rejects null", () => {
       // `const` is conjunctive with its siblings, not an override: both of
       // these reject every value, so claiming nullability would let the
diff --git a/core/json/nullableUnion.ts b/core/json/nullableUnion.ts
index 3217b0f1..fd6761dc 100644
--- a/core/json/nullableUnion.ts
+++ b/core/json/nullableUnion.ts
@@ -454,6 +454,9 @@ function anyOfAdmitsNull(schema: NullableUnionSchema): boolean {
   const branches = schema.anyOf;
   if (!Array.isArray(branches)) return false;
   return branches.some((entry) => {
+    // JSON Schema's boolean form: `true` is the unconstrained schema and admits
+    // every value, `null` among them, while `false` admits none.
+    if (typeof entry === "boolean") return entry;
     const branch = toBranch(entry);
     if (branch === null) return false;
     const branchSchema = branch as NullableUnionSchema;