diff --git a/actor.ts b/actor.ts
index 80faa28..5786122 100644
--- a/actor.ts
+++ b/actor.ts
@@ -131,9 +131,7 @@ export class Turn {
     assert(ref: Ref, assertion: Assertion): Handle {
         const h = nextHandle++;
         this.enqueue(ref.relay, t => {
-            const a = ref.attenuation === void 0
-                ? assertion
-                : runRewrites(ref.attenuation, assertion);
+            const a = runRewrites(ref.attenuation, assertion);
             if (a !== null) {
                 this.actor.outbound.set(h, ref);
                 ref.target.assert?.(t, a, h);
@@ -167,9 +165,7 @@ export class Turn {
     }
 
     message(ref: Ref, assertion: Assertion): void {
-        const a = ref.attenuation === void 0
-            ? assertion
-            : runRewrites(ref.attenuation, assertion);
+        const a = runRewrites(ref.attenuation, assertion);
         if (a !== null) this.enqueue(ref.relay, t => ref.target.message?.(t, assertion));
     }
 
@@ -261,11 +257,13 @@ export function rewrite(r: Rewrite, v: Assertion): Assertion | null {
     return instantiate(r.template, bindings);
 }
 
-export function runRewrites(a: Attenuation, v: Assertion): Assertion | null {
-    for (const r of a) {
-        const w = rewrite(r, v);
-        if (w === null) return null;
-        v = w;
+export function runRewrites(a: Attenuation | undefined, v: Assertion): Assertion | null {
+    if (a !== void 0) {
+        for (const r of a) {
+            const w = rewrite(r, v);
+            if (w === null) return null;
+            v = w;
+        }
     }
     return v;
 }