diff --git a/scripts/run-additional-boundary-checks.mjs b/scripts/run-additional-boundary-checks.mjs
index 097adada7039..6e22195feac9 100644
--- a/scripts/run-additional-boundary-checks.mjs
+++ b/scripts/run-additional-boundary-checks.mjs
@@ -105,11 +105,11 @@ export function parseShardSpec(value) {
   if (!match) {
     throw new Error(`Invalid shard spec '${value}' (expected N/TOTAL)`);
   }
-  const index = Number.parseInt(match[1], 10);
-  const count = Number.parseInt(match[2], 10);
+  const index = Number(match[1]);
+  const count = Number(match[2]);
   if (
-    !Number.isInteger(index) ||
-    !Number.isInteger(count) ||
+    !Number.isSafeInteger(index) ||
+    !Number.isSafeInteger(count) ||
     index < 1 ||
     count < 1 ||
     index > count
diff --git a/test/scripts/run-additional-boundary-checks.test.ts b/test/scripts/run-additional-boundary-checks.test.ts
index 9aa3abf0b89a..6efcf60806ba 100644
--- a/test/scripts/run-additional-boundary-checks.test.ts
+++ b/test/scripts/run-additional-boundary-checks.test.ts
@@ -91,6 +91,7 @@ describe("run-additional-boundary-checks", () => {
     );
     expect(new Set(shardedLabels).size).toBe(BOUNDARY_CHECKS.length);
     expect(() => parseShardSpec("5/4")).toThrow("Invalid shard spec");
+    expect(() => parseShardSpec("9007199254740993/9007199254740994")).toThrow("Invalid shard spec");
   });
 
   it("keeps the raw HTTP/2 import guard in source boundary checks", () => {