diff --git a/pr-checks/post-comment.test.ts b/pr-checks/post-comment.test.ts
index 8c1ad5d83..d82f5d249 100644
--- a/pr-checks/post-comment.test.ts
+++ b/pr-checks/post-comment.test.ts
@@ -64,14 +64,14 @@ describe("parseOptions", async () => {
   await it("rejects an empty --marker", () => {
     assert.throws(
       () => parseOptions(withFlag("--marker", "")),
-      /Missing required flag --marker/,
+      /The value for --marker cannot be empty/,
     );
   });
 
   await it("rejects a whitespace-only --marker", () => {
     assert.throws(
       () => parseOptions(withFlag("--marker", " \t\n")),
-      /Missing required flag --marker/,
+      /The value for --marker cannot be empty/,
     );
   });
 });
diff --git a/pr-checks/post-comment.ts b/pr-checks/post-comment.ts
index 8c9703357..20dad0cf0 100644
--- a/pr-checks/post-comment.ts
+++ b/pr-checks/post-comment.ts
@@ -46,12 +46,16 @@ export function parseOptions(argv?: string[]): Options {
     strict: true,
   });
 
-  assert(values.marker?.trim(), "Missing required flag --marker.");
+  assert(values.marker !== undefined, "Missing required flag --marker.");
+  assert(
+    values.marker.trim() !== "",
+    "The value for --marker cannot be empty.",
+  );
   const [owner, repo] = values.repository!.split("/");
 
   return {
     body: values.body!,
-    marker: values.marker!,
+    marker: values.marker,
     issueId: Number(values["issue-id"]),
     repository: { owner, repo },
   };