diff --git a/glue/crumble/circuit/propagated_pauli_frames.js b/glue/crumble/circuit/propagated_pauli_frames.js
index 2a65df42f..e51d35c3b 100644
--- a/glue/crumble/circuit/propagated_pauli_frames.js
+++ b/glue/crumble/circuit/propagated_pauli_frames.js
@@ -55,7 +55,7 @@ class PropagatedPauliFrameLayer {
         for (let q of this.errors) {
             num_qubits = Math.max(num_qubits, q + 1);
         }
-        for (let [q1, q2] of this.crossings) {
+        for (const {q1, q2} of this.crossings) {
             num_qubits = Math.max(num_qubits, q1 + 1);
             num_qubits = Math.max(num_qubits, q2 + 1);
         }
diff --git a/glue/crumble/circuit/propagated_pauli_frames.tostring.test.js b/glue/crumble/circuit/propagated_pauli_frames.tostring.test.js
new file mode 100644
index 000000000..af978d354
--- /dev/null
+++ b/glue/crumble/circuit/propagated_pauli_frames.tostring.test.js
@@ -0,0 +1,12 @@
+import {test, assertThat} from "../test/test_util.js";
+import {PropagatedPauliFrameLayer} from "./propagated_pauli_frames.js";
+
+test("propagated_pauli_frame_layer.toString_handles_object_crossings", () => {
+    const layer = new PropagatedPauliFrameLayer(
+        new Map([[0, 'X']]),
+        new Set(),
+        [{q1: 0, q2: 1, color: 'X'}],
+    );
+    assertThat(() => String(layer)).runsWithoutThrowingAnException();
+});
+