diff --git a/fastapi/_compat.py b/fastapi/_compat.py
index 227ad837d..6e9a6f0ed 100644
--- a/fastapi/_compat.py
+++ b/fastapi/_compat.py
@@ -246,7 +246,21 @@ if PYDANTIC_V2:
         ) and not isinstance(field.field_info, params.Body)
 
     def is_sequence_field(field: ModelField) -> bool:
-        return field_annotation_is_sequence(field.field_info.annotation)
+        return field_annotation_is_sequence(
+            field.field_info.annotation
+        ) or field_annotation_is_optional_sequence(field.field_info.annotation)
+
+    def field_annotation_is_optional_sequence(
+        annotation: Union[Type[Any], None],
+    ) -> bool:
+        origin = get_origin(annotation)
+        if origin is Union:
+            args = get_args(annotation)
+            for arg in args:
+                if hasattr(arg, "__origin__"):
+                    if arg.__origin__ in sequence_types:
+                        return True
+        return False
 
     def is_scalar_sequence_field(field: ModelField) -> bool:
         return field_annotation_is_scalar_sequence(field.field_info.annotation)
diff --git a/tests/test_compat.py b/tests/test_compat.py
index f4a3093c5..c05e5ddad 100644
--- a/tests/test_compat.py
+++ b/tests/test_compat.py
@@ -1,4 +1,4 @@
-from typing import Any, Dict, List, Union
+from typing import Any, Dict, FrozenSet, List, Optional, Set, Union
 
 from fastapi import FastAPI, UploadFile
 from fastapi._compat import (
@@ -9,6 +9,7 @@ from fastapi._compat import (
     get_model_fields,
     is_bytes_sequence_annotation,
     is_scalar_field,
+    is_sequence_field,
     is_uploadfile_sequence_annotation,
 )
 from fastapi.testclient import TestClient
@@ -96,6 +97,27 @@ def test_is_uploadfile_sequence_annotation():
     assert is_uploadfile_sequence_annotation(Union[List[str], List[UploadFile]])
 
 
+@needs_pydanticv2
+def test_model_optional_union_v2():
+    # For coverage
+    types = [
+        Optional[List[str]],
+        Union[List[int], List[float]],
+        Optional[Set[int]],
+        Union[Set[int], Set[float]],
+        Optional[FrozenSet[int]],
+        Union[List[int], None],
+    ]
+    for annotation in types:
+        field_info = FieldInfo(annotation=annotation)
+        field = ModelField(name="foo", field_info=field_info)
+        assert is_sequence_field(field) is True
+
+    field_info_str = FieldInfo(annotation=str)
+    field_str = ModelField(name="foo", field_info=field_info_str)
+    assert is_sequence_field(field_str) is False
+
+
 def test_is_pv1_scalar_field():
     # For coverage
     class Model(BaseModel):