diff --git a/tests/magicdata/Include/internal/pycore_magic_number.h b/tests/magicdata/Include/internal/pycore_magic_number.h
new file mode 100644
index 0000000..e7c1893
--- /dev/null
+++ b/tests/magicdata/Include/internal/pycore_magic_number.h
@@ -0,0 +1,11 @@
+// copied from cpython bd3d31f380cd451a4ab6da5fbfde463fed95b5b5
+// ...
+
+#ifndef Py_INTERNAL_MAGIC_NUMBER_H
+#define Py_INTERNAL_MAGIC_NUMBER_H
+
+#define PYC_MAGIC_NUMBER 3603
+
+#endif  // !Py_INTERNAL_MAGIC_NUMBER_H
+
+// ...
diff --git a/tests/test_run_release.py b/tests/test_run_release.py
index 7268ccf..8f545bd 100644
--- a/tests/test_run_release.py
+++ b/tests/test_run_release.py
@@ -1,6 +1,10 @@
+from pathlib import Path
+from typing import cast
+
 import pytest
 
 import run_release
+from release import ReleaseShelf, Tag
 
 
 @pytest.mark.parametrize(
@@ -22,3 +26,14 @@ def test_invalid_extract_github_owner() -> None:
         "https://example.com",
     ):
         run_release.extract_github_owner("https://example.com")
+
+
+def test_check_magic_number() -> None:
+    db = {
+        "release": Tag("3.13.0rc1"),
+        "git_repo": str(Path(__file__).parent / "magicdata"),
+    }
+    with pytest.raises(
+        run_release.ReleaseException, match="Magic numbers in .* don't match"
+    ):
+        run_release.check_magic_number(cast(ReleaseShelf, db))