diff --git a/.tsan-suppressions b/.tsan-suppressions
index 732650486b8..3a04c1c6bde 100644
--- a/.tsan-suppressions
+++ b/.tsan-suppressions
@@ -1,2 +1 @@
 race:mongoc_counter*
-race:_mongoc_handshake_freeze
diff --git a/src/libmongoc/src/mongoc/mongoc-handshake.c b/src/libmongoc/src/mongoc/mongoc-handshake.c
index 2d711252088..9622b6d09f0 100644
--- a/src/libmongoc/src/mongoc/mongoc-handshake.c
+++ b/src/libmongoc/src/mongoc/mongoc-handshake.c
@@ -726,7 +726,9 @@ _mongoc_handshake_build_doc_with_application (const char *appname)
 void
 _mongoc_handshake_freeze (void)
 {
+   bson_mutex_lock (&gHandshakeLock);
    _mongoc_handshake_get ()->frozen = true;
+   bson_mutex_unlock (&gHandshakeLock);
 }
 
 /*