diff --git a/skills/rig/rig.ts b/skills/rig/rig.ts
index 34ab2e0..1bf3059 100644
--- a/skills/rig/rig.ts
+++ b/skills/rig/rig.ts
@@ -1687,6 +1687,10 @@ function assertValidSchema(schema: Schema, agentName: string, slot: "input" | "o
     assertValidSchema(schema.additionalProperties, agentName, slot, `${path}.*`);
     return;
   }
+  if ("nullable" in schema && schema.nullable === true) {
+    assertValidSchema((schema as NullableSchema).inner, agentName, slot, path);
+    return;
+  }
   if ("properties" in schema) {
     for (const [key, value] of Object.entries(schema.properties) as [string, Schema][]) {
       assertValidSchema(value, agentName, slot, `${path}.${key}`);
diff --git a/src/rig.test.ts b/src/rig.test.ts
index 741323d..86ba91f 100644
--- a/src/rig.test.ts
+++ b/src/rig.test.ts
@@ -141,6 +141,11 @@ describe("agent", () => {
       name: "implicit-nested",
       input: s.object({ text: "go" as any }),
     })).toThrow(/input\.text/);
+
+    expect(() => agent({
+      name: "implicit-nullable-nested",
+      output: s.nullable(s.object({ score: "bad" as any })),
+    })).toThrow(/output\.score/);
   });
 
   it("does not expose deprecated hook APIs in core", () => {