diff --git a/fastapi/encoders.py b/fastapi/encoders.py
index 43f24101b6..329f96ace2 100644
--- a/fastapi/encoders.py
+++ b/fastapi/encoders.py
@@ -280,11 +280,13 @@ def jsonable_encoder(
         return None
     if isinstance(obj, dict):
         encoded_dict = {}
-        allowed_keys = set(obj.keys())
-        if include is not None:
-            allowed_keys &= set(include)
-        if exclude is not None:
-            allowed_keys -= set(exclude)
+        allowed_keys: set[Any] | None = None
+        if include is not None or exclude is not None:
+            allowed_keys = set(obj.keys())
+            if include is not None:
+                allowed_keys &= set(include)
+            if exclude is not None:
+                allowed_keys -= set(exclude)
         for key, value in obj.items():
             if (
                 (
@@ -293,7 +295,7 @@ def jsonable_encoder(
                     or (not key.startswith("_sa"))
                 )
                 and (value is not None or not exclude_none)
-                and key in allowed_keys
+                and (allowed_keys is None or key in allowed_keys)
             ):
                 encoded_key = jsonable_encoder(
                     key,
diff --git a/tests/test_jsonable_encoder.py b/tests/test_jsonable_encoder.py
index c23a9e5d79..dde6fe3f8e 100644
--- a/tests/test_jsonable_encoder.py
+++ b/tests/test_jsonable_encoder.py
@@ -329,3 +329,41 @@ def test_encode_color(module_path):
 
     data = {"color": Color("blue")}
     assert jsonable_encoder(data) == {"color": "blue"}
+
+
+def test_dict_no_filter_returns_all_keys():
+    result = jsonable_encoder({"a": 1, "b": 2, "c": 3})
+    assert result == {"a": 1, "b": 2, "c": 3}
+
+
+def test_dict_include_filters_correctly():
+    result = jsonable_encoder({"a": 1, "b": 2}, include={"a"})
+    assert result == {"a": 1}
+
+
+def test_dict_exclude_filters_correctly():
+    result = jsonable_encoder({"a": 1, "b": 2}, exclude={"b"})
+    assert result == {"a": 1}
+
+
+def test_dict_empty_include_returns_empty():
+    result = jsonable_encoder({"a": 1}, include=set())
+    assert result == {}
+
+
+def test_dict_empty_exclude_returns_all():
+    result = jsonable_encoder({"a": 1}, exclude=set())
+    assert result == {"a": 1}
+
+
+def test_dict_both_include_and_exclude():
+    result = jsonable_encoder(
+        {"a": 1, "b": 2, "c": 3}, include={"a", "b"}, exclude={"b"}
+    )
+    assert result == {"a": 1}
+
+
+def test_encode_nested_dict():
+    nested = {"level1": {"level2": {"level3": 42}}}
+    result = jsonable_encoder(nested)
+    assert result == nested