diff --git a/packages/runtime/src/scr_util_callable.c b/packages/runtime/src/scr_util_callable.c
index df6a68272..574b9d423 100644
--- a/packages/runtime/src/scr_util_callable.c
+++ b/packages/runtime/src/scr_util_callable.c
@@ -881,6 +881,17 @@ ScrDyn *scr_util_diff(ScrDyn *actual, ScrDyn *expected) {
     scr_throw_error_msg_code(SCR_ERR_RANGE, message, (size_t)n, "ERR_OUT_OF_RANGE");
     return NULL;
   }
+  /* Two distinct empty sequences: Node's myersDiff reads past its
+   * one-element state, finds no end and answers undefined, which the
+   * ArrayPrototypeReverse of util.diff rejects. The trace below would be read
+   * out of bounds. */
+  if (max == 0) {
+    uc_diff_seq_free(&a);
+    uc_diff_seq_free(&e);
+    static const char message[] = "Cannot convert undefined or null to object";
+    scr_throw_error_msg(SCR_ERR_TYPE, message, sizeof message - 1);
+    return NULL;
+  }
   size_t width = 2 * max + 1;
   int32_t *v = calloc(width, sizeof *v);
   int32_t **trace = malloc((max + 1) * sizeof *trace);
diff --git a/tests/corpus/7705-util-diff.cjs b/tests/corpus/7705-util-diff.cjs
index 9e52fd165..489586a3b 100644
--- a/tests/corpus/7705-util-diff.cjs
+++ b/tests/corpus/7705-util-diff.cjs
@@ -7,7 +7,7 @@ const show = (a, e) => {
   try { console.log(JSON.stringify(util.diff(a, e))); } catch (err) { console.log(err.name, err.code, err.message); }
 };
 show("abc", "abd"); show("kitten", "sitting"); show("", "x"); show("same", "same"); show("", "");
-show(["a", "b", "c"], ["a", "c", "d"]); show(["x"], []); show([], ["y", "z"]);
+show(["a", "b", "c"], ["a", "c", "d"]); show(["x"], []); show([], ["y", "z"]); show([], []);
 const arr = ["p"]; show(arr, arr); show(1, 1); show(1, 2); show("a", 2); show(["a", 1], ["a"]); show(["a"], [, "b"]);
 show(null, "x"); show("x", undefined); show("héllo😀", "hello😀"); show({}, "x");
 show("the quick brown fox", "the quack brown box");