diff --git a/sqlmodel/main.py b/sqlmodel/main.py
index 9a1a676775..3cd7b8388e 100644
--- a/sqlmodel/main.py
+++ b/sqlmodel/main.py
@@ -200,7 +200,7 @@ def __init__(
         self.sa_relationship_kwargs = sa_relationship_kwargs
 
 
-@dataclass
+@dataclass(unsafe_hash=True)
 class FieldInfoMetadata:
     primary_key: bool | UndefinedType = Undefined
     nullable: bool | UndefinedType = Undefined
diff --git a/tests/test_field_info_metadata_hashable.py b/tests/test_field_info_metadata_hashable.py
new file mode 100644
index 0000000000..da32a1b6b6
--- /dev/null
+++ b/tests/test_field_info_metadata_hashable.py
@@ -0,0 +1,29 @@
+from typing import Annotated
+
+from sqlmodel import Field
+from sqlmodel.main import FieldInfoMetadata
+
+
+def test_field_info_metadata_is_hashable():
+    """FieldInfoMetadata must be hashable so that Annotated types containing it
+    can be used in sets (e.g. FastAPI's OpenAPI schema generation)."""
+    meta = FieldInfoMetadata(primary_key=True)
+    hash(meta)
+
+
+def test_annotated_with_field_info_metadata_in_set():
+    """Annotated types carrying FieldInfoMetadata must work inside a set,
+    which is required by FastAPI's get_definitions()."""
+    t = Annotated[int, FieldInfoMetadata(unique=True)]
+    s = {t}
+    assert t in s
+
+
+def test_annotated_field_type_in_set():
+    """Realistic scenario: custom Annotated field aliases used in a set."""
+    PositiveInt = Annotated[int, Field(ge=0)]
+    ShortStr = Annotated[str, Field(max_length=32)]
+
+    s = {PositiveInt, ShortStr}
+    assert PositiveInt in s
+    assert ShortStr in s