diff --git a/modules/mesh-vault/cmd/mesh-vault/intake.go b/modules/mesh-vault/cmd/mesh-vault/intake.go
index b8a03715..9b5648ad 100644
--- a/modules/mesh-vault/cmd/mesh-vault/intake.go
+++ b/modules/mesh-vault/cmd/mesh-vault/intake.go
@@ -728,6 +728,10 @@ func (v *Vault) RotateFor(caller, secret string, one Narrow, by, why string) (Ch
 		return Changed{}, fmt.Errorf("not rotated: %s is a bus account the controller mints and hands here (ADR 0374 "+
 			"clause 4): only a password whose hash the bus's user list holds can log in, so the vault makes no new "+
 			"value for it; `module issue` again hands a new one and replaces this in place", secret)
+	case isLedgersSecret(secret):
+		return Changed{}, fmt.Errorf("not rotated: %s is the tool runner's own secret of the ledger accounts of its machine, "+
+			"which the vault rewrites on each ledger account minted or retired (ADR 0597 §9); a person's rotation would "+
+			"replace every module's credential with a value no ledger account holds", secret)
 	case rec.Origin == OriginIssued:
 		return Changed{}, fmt.Errorf("not rotated: %s is issued by its provider's software, which the mesh cannot "+
 			"make or rotate (ADR 0305 §9): change it in that software, and `secret issued` takes the value it holds now",
diff --git a/modules/mesh-vault/cmd/mesh-vault/ledgers.go b/modules/mesh-vault/cmd/mesh-vault/ledgers.go
index e329ed5b..65067bff 100644
--- a/modules/mesh-vault/cmd/mesh-vault/ledgers.go
+++ b/modules/mesh-vault/cmd/mesh-vault/ledgers.go
@@ -26,6 +26,12 @@ func ledgersSecret(node string) (string, error) {
 	return OwnSecret(node, toolRunnerModule, buscompose.LedgersSecret)
 }
 
+// isLedgersSecret says secret is a machine's `ledgers`: `own/<node>/node-tools/ledgers`.
+func isLedgersSecret(secret string) bool {
+	parts := strings.Split(secret, "/")
+	return len(parts) == 4 && parts[0] == "own" && parts[2] == toolRunnerModule && parts[3] == buscompose.LedgersSecret
+}
+
 // toolRunnerNodes are the machines whose tool runner is wanted, sorted.
 func (v *Vault) toolRunnerNodes() []string {
 	v.minting.mu.Lock()
diff --git a/modules/mesh-vault/cmd/mesh-vault/mint_test.go b/modules/mesh-vault/cmd/mesh-vault/mint_test.go
index e380c69d..697ab901 100644
--- a/modules/mesh-vault/cmd/mesh-vault/mint_test.go
+++ b/modules/mesh-vault/cmd/mesh-vault/mint_test.go
@@ -196,6 +196,21 @@ func TestTheVaultMintsAWantedAccountOnceAndNothingItHolds(t *testing.T) {
 					t.Errorf("wanted again, m is not back in ledgers (%d) with its hash", len(got))
 				}
 			}},
+			// 1966/CAT-V2 (ADR 0597 §9): a person's rotate of a machine's `ledgers` is refused as a bus account's is: it
+			// would replace every module's credential with a value no ledger account holds.
+			{"a person's rotate of ledgers is refused", func(t *testing.T, v testVault, accounts *fakeAccounts, priv string) {
+				w := nodeToolsWant("ace")
+				v.WantHeard(w.User, wantRaw(t, w), false)
+				v.LedgersPass()
+				before, _ := ledgersOf(t, v, priv)
+				if _, err := v.Rotate("person.jochen", "own/ace/node-tools/ledgers", "jochen", "a test"); err == nil ||
+					!strings.Contains(err.Error(), "ledger accounts of its machine") {
+					t.Errorf("a person rotated ledgers: %v", err)
+				}
+				if after, _ := ledgersOf(t, v, priv); len(after) != len(before) {
+					t.Errorf("a refused rotation changed ledgers: %d, was %d", len(after), len(before))
+				}
+			}},
 		} {
 			t.Run(c.name, func(t *testing.T) {
 				v, accounts, priv := mintingVault(t)