diff --git a/tagging/update_wiki.py b/tagging/update_wiki.py
index 70b39338c7..193558c8df 100755
--- a/tagging/update_wiki.py
+++ b/tagging/update_wiki.py
@@ -18,6 +18,7 @@ def update_home_wiki_page(wiki_dir: Path, month: str) -> None:
     wiki_home_content = wiki_home_file.read_text()
     month_line = f"| [`{month}`](./{month}) |\n"
     if month_line not in wiki_home_content:
+        assert TABLE_BEGINNING in wiki_home_content
         wiki_home_content = wiki_home_content.replace(
             TABLE_BEGINNING, TABLE_BEGINNING + month_line
         )
@@ -39,7 +40,9 @@ def update_monthly_wiki_page(
         monthly_page.write_text(MONTHLY_PAGE_HEADER)
         LOGGER.info(f"Created monthly page: {monthly_page.relative_to(wiki_dir)}")
 
-    monthly_page_content = monthly_page.read_text().replace(
+    monthly_page_content = monthly_page.read_text()
+    assert MONTHLY_PAGE_HEADER in monthly_page_content
+    monthly_page_content = monthly_page_content.replace(
         MONTHLY_PAGE_HEADER, MONTHLY_PAGE_HEADER + build_history_line + "\n"
     )
     monthly_page.write_text(monthly_page_content)