diff --git a/docs/migration/draft-v9-migration-guide.md b/docs/migration/draft-v9-migration-guide.md
index dba02dcdd509..c543009d4995 100644
--- a/docs/migration/draft-v9-migration-guide.md
+++ b/docs/migration/draft-v9-migration-guide.md
@@ -17,6 +17,7 @@
 - Deprecated `memoBuilder`. No replacements.
 - Deprecated `BAGGAGE_HEADER_NAME`. No replacements.
 - Deprecated `makeFifoCache`. No replacements.
+- Deprecated `flatten`. No replacements.
 
 ## `@sentry/core`