diff --git a/src/callers/index.ts b/src/callers/index.ts
index 6ed8fa10..8a913775 100644
--- a/src/callers/index.ts
+++ b/src/callers/index.ts
@@ -179,12 +179,28 @@ export function parseConfiguredVerbCallers(raw: unknown, verbs: readonly string[
 const callerWords = ["operator", "healers", "persons", "sessions", "invokers"];
 const callerForm = /^(seat:[a-z][a-z0-9-]*|module:[a-z][a-z0-9-]*|holder:[a-z][a-z0-9-]*@same-node)$/;
 
+/**
+ * The callers a verb that names none takes by its class (design 47 G §391, §456), as the Go reader's DefaultCallers: a
+ * `read` takes invokers, persons and sessions; an `act` the operator and sessions; a `warrant` the operator. A verb that
+ * names no class is a `read`.
+ */
+function defaultCallers(cls: string | undefined): readonly string[] {
+  switch (cls) {
+    case "act":
+      return ["operator", "sessions"];
+    case "warrant":
+      return ["operator"];
+  }
+  return ["invokers", "persons", "sessions"];
+}
+
 /**
  * The callers a seat definition names for a verb or an accepted kind (design 47 G §336, §392): a list of entries, each
  * one of the forms the format knows. Text is refused naming the verb, and so is an entry that is no form (a bare name
- * among them), as the Go reader does.
+ * among them), as the Go reader does. A verb that names no callers takes the default of its class `cls` (§391).
  */
-export function readDefinitionCallers(verb: string, value: unknown): readonly string[] {
+export function readDefinitionCallers(verb: string, value: unknown, cls?: string): readonly string[] {
+  if (value === undefined || value === null) return defaultCallers(cls);
   if (typeof value === "string") {
     throw new Error(`${verb}: callers are text ("${value}"): a definition gives its callers as a list`);
   }
diff --git a/test/sdk.test.ts b/test/sdk.test.ts
index 8f59871e..f1fd618c 100644
--- a/test/sdk.test.ts
+++ b/test/sdk.test.ts
@@ -682,6 +682,13 @@ test("callers and verb callers judge a proved caller by the Go side's rules (ADR
     ["operator", "invokers", "seat:mesh-grants", "holder:node-backup@same-node"]);
   assert.throws(() => readDefinitionCallers("list", "a person"), /list: callers are text/);
   assert.throws(() => readDefinitionCallers("list", ["mesh-grants"]), /list: the callers entry "mesh-grants" is none of/);
+  // design 47 G §391, §456: a verb with no callers takes its class's default; no class reads as read; its own list is kept
+  const byClass: [string | undefined, string[]][] = [
+    [undefined, ["invokers", "persons", "sessions"]], ["read", ["invokers", "persons", "sessions"]],
+    ["act", ["operator", "sessions"]], ["warrant", ["operator"]],
+  ];
+  for (const [cls, want] of byClass) assert.deepEqual(readDefinitionCallers("list", undefined, cls), want, String(cls));
+  assert.deepEqual(readDefinitionCallers("register", ["seat:mesh-broker"], "act"), ["seat:mesh-broker"]);
   assert.throws(() => parseCallers('{"callers":["a"],"more":1}'), /unknown field "more"/);
 
   const verbs = parseVerbCallers('{"pull":["*"],"merge-pull":["mesh-delivery-forge-bridge"],"comment":["operator"]}', ["pull", "merge-pull", "comment"], {});