diff --git a/sqlglot/optimizer/merge_subqueries.py b/sqlglot/optimizer/merge_subqueries.py
index 603f5df0c4..866f78c239 100644
--- a/sqlglot/optimizer/merge_subqueries.py
+++ b/sqlglot/optimizer/merge_subqueries.py
@@ -227,10 +227,13 @@ def _rename_inner_sources(outer_scope, inner_scope, alias):
         inner_scope (sqlglot.optimizer.scope.Scope)
         alias (str)
     """
-    taken = set(outer_scope.selected_sources)
-    conflicts = taken.intersection(set(inner_scope.selected_sources))
+    inner_taken = set(inner_scope.selected_sources)
+    outer_taken = set(outer_scope.selected_sources)
+    conflicts = outer_taken.intersection(inner_taken)
     conflicts -= {alias}
 
+    taken = outer_taken.union(inner_taken)
+
     for conflict in conflicts:
         new_name = find_new_name(taken, conflict)
 
diff --git a/tests/fixtures/optimizer/merge_subqueries.sql b/tests/fixtures/optimizer/merge_subqueries.sql
index ce5a435119..e39e7d1709 100644
--- a/tests/fixtures/optimizer/merge_subqueries.sql
+++ b/tests/fixtures/optimizer/merge_subqueries.sql
@@ -446,3 +446,21 @@ SELECT
   1 AS a;
 WITH q AS (SELECT x.a AS a FROM x AS x ORDER BY x.a) SELECT q.a AS a FROM q AS q UNION ALL SELECT 1 AS a;
 
+# title: Consecutive inner - outer conflicting names
+WITH tbl AS (select 1 as id)
+SELECT
+  id
+FROM (
+  SELECT OTBL.id
+  FROM (
+    SELECT OTBL.id
+    FROM (
+      SELECT OTBL.id
+      FROM tbl AS OTBL
+      LEFT OUTER JOIN tbl AS ITBL ON OTBL.id = ITBL.id
+    ) AS OTBL
+    LEFT OUTER JOIN tbl AS ITBL ON OTBL.id = ITBL.id
+  ) AS OTBL
+  LEFT OUTER JOIN tbl AS ITBL ON OTBL.id = ITBL.id
+) AS ITBL;
+WITH tbl AS (SELECT 1 AS id) SELECT OTBL.id AS id FROM tbl AS OTBL LEFT OUTER JOIN tbl AS ITBL_2 ON OTBL.id = ITBL_2.id LEFT OUTER JOIN tbl AS ITBL_3 ON OTBL.id = ITBL_3.id LEFT OUTER JOIN tbl AS ITBL ON OTBL.id = ITBL.id;