diff --git a/tests/main-missing-repository.test.js b/tests/main-missing-repository.test.js
new file mode 100644
index 0000000..7bec9a8
--- /dev/null
+++ b/tests/main-missing-repository.test.js
@@ -0,0 +1,12 @@
+// Verify `main` exits with an error when `GITHUB_REPOSITORY` is missing.
+// @ts-check
+
+delete process.env.GITHUB_REPOSITORY;
+
+(async () => {
+  try {
+    await import("../main.js");
+  } catch (error) {
+    console.error(error.message);
+  }
+})();
diff --git a/tests/snapshots/index.js.md b/tests/snapshots/index.js.md
index 652824d..a8cfc23 100644
--- a/tests/snapshots/index.js.md
+++ b/tests/snapshots/index.js.md
@@ -4,6 +4,16 @@ The actual snapshot is saved in `index.js.snap`.
 
 Generated by [AVA](https://avajs.dev).
 
+## main-missing-repository.test.js
+
+> stderr
+
+    'GITHUB_REPOSITORY missing, must be set to \'<owner>/<repo>\''
+
+> stdout
+
+    ''
+
 ## post-token-set.test.js
 
 > stderr
diff --git a/tests/snapshots/index.js.snap b/tests/snapshots/index.js.snap
index e33d42d..3e3f2e6 100644
Binary files a/tests/snapshots/index.js.snap and b/tests/snapshots/index.js.snap differ