diff --git a/README.md b/README.md
index ba8a6151..e8f5e618 100644
--- a/README.md
+++ b/README.md
@@ -21,7 +21,7 @@ This project is a fork of [Dorthu/openapi3](https://github.com/Dorthu/openapi3/)
     * recursive schemas (A.a -> A)
   * request body model creation via pydantic
     * pydantic compatible "format"-type coercion (e.g. datetime.interval)
-    * additionalProperties (limited to string-to-any dictionaries without properties)
+    * additionalProperties (string-to-any dictionaries, including inline schemas with `allOf`/`nullable`)
   * response body & header parsing via pydantic
   * blocking and nonblocking (asyncio) interface via [httpx](https://www.python-httpx.org/)
     * SOCKS5 via socksio
diff --git a/src/aiopenapi3/model.py b/src/aiopenapi3/model.py
index 64f682a6..15a9779e 100644
--- a/src/aiopenapi3/model.py
+++ b/src/aiopenapi3/model.py
@@ -618,9 +618,10 @@ def createAnnotation(
 
     @staticmethod
     def types(schema: "SchemaType") -> typing.Generator[str, None, None]:
+        nullable = getattr(schema, "nullable", False)
         if isinstance(schema.type, str):
             yield schema.type
-            if getattr(schema, "nullable", False):
+            if nullable:
                 yield "null"
         else:
             typesfilter: set[str] = set()
@@ -631,6 +632,9 @@ def types(schema: "SchemaType") -> typing.Generator[str, None, None]:
                 values = set(SCHEMA_TYPES)
                 typesfilter = set()
 
+                if nullable:
+                    typesfilter.add("null")
+
                 if (const := getattr(schema, "const", None)) is not None:
                     typesfilter.add(cast(str, TYPES_SCHEMA_MAP.get(type(const))))
 
diff --git a/src/aiopenapi3/openapi.py b/src/aiopenapi3/openapi.py
index 6e26fbcc..00156fb0 100644
--- a/src/aiopenapi3/openapi.py
+++ b/src/aiopenapi3/openapi.py
@@ -449,6 +449,7 @@ def _init_operationindex(self, use_operation_tags: bool) -> bool:
     def _get_combined_attributes(schema):
         """Combine attributes from the schema."""
         is_array = Model.is_type_any(schema) or Model.is_type(schema, "array")
+        additional = getattr(schema, "additionalProperties", None)
         return (
             getattr(schema, "oneOf", [])  # Swagger compat
             + (
@@ -462,6 +463,7 @@ def _get_combined_attributes(schema):
             + ([schema.items] if is_array and schema.items is not None and not isinstance(schema, list) else [])
             + (schema.items if is_array and schema.items is not None and isinstance(schema, list) else [])
             + (getattr(schema, "prefixItems", []) or [] if is_array else [])
+            + ([additional] if isinstance(additional, (SchemaBase, ReferenceBase)) else [])
         )
 
     @classmethod
diff --git a/tests/conftest.py b/tests/conftest.py
index 3e572219..26bfea31 100644
--- a/tests/conftest.py
+++ b/tests/conftest.py
@@ -449,6 +449,11 @@ def with_schema_additionalProperties_and_named_properties():
     yield _get_parsed_yaml("schema-additionalProperties-and-named-properties.yaml")
 
 
+@pytest.fixture
+def with_schema_additionalProperties_nullable_allof():
+    yield _get_parsed_yaml("schema-additionalProperties-nullable-allof.yaml")
+
+
 @pytest.fixture
 def with_schema_date_types():
     yield _get_parsed_yaml("schema-date-types.yaml")
diff --git a/tests/fixtures/schema-additionalProperties-nullable-allof.yaml b/tests/fixtures/schema-additionalProperties-nullable-allof.yaml
new file mode 100644
index 00000000..6538497c
--- /dev/null
+++ b/tests/fixtures/schema-additionalProperties-nullable-allof.yaml
@@ -0,0 +1,64 @@
+openapi: "3.0.3"
+info:
+  version: 1.0.0
+  title: additionalProperties nullable allOf
+
+components:
+  schemas:
+    A:
+      type: object
+      nullable: false
+      additionalProperties: false
+      properties:
+        a:
+          type: string
+      required:
+        - a
+
+paths:
+  /implicit-nullable-object-allOf:
+    get:
+      operationId: implicit-allOf
+      responses:
+        "200":
+          description: ok
+          content:
+            application/json:
+              schema:
+                type: object
+                additionalProperties:
+                  # type: object - not set
+                  nullable: true
+                  allOf:
+                    - $ref: "#/components/schemas/A"
+
+  /explicit-nullable-object-allOf:
+    get:
+      operationId: explicit-allOf
+      responses:
+        "200":
+          description: ok
+          content:
+            application/json:
+              schema:
+                type: object
+                additionalProperties:
+                  type: object
+                  nullable: true
+                  allOf:
+                    - $ref: "#/components/schemas/A"
+
+  /explicit-object-oneOf-nullable:
+    get:
+      operationId: explicit-oneOf
+      responses:
+        "200":
+          description: ok
+          content:
+            application/json:
+              schema:
+                type: object
+                additionalProperties:
+                  oneOf:
+                    - $ref: "#/components/schemas/A"
+                    - nullable: true
diff --git a/tests/schema_test.py b/tests/schema_test.py
index 05db6be8..f93136ba 100644
--- a/tests/schema_test.py
+++ b/tests/schema_test.py
@@ -332,6 +332,27 @@ def test_schema_with_additionalProperties_and_named_properties(with_schema_addit
     assert b.aio3_additionalProperties["foo"] == "bar"
 
 
+def test_schema_additionalProperties_nullable_allof(with_schema_additionalProperties_nullable_allof):
+    """
+    Inline additionalProperties schema with nullable+allOf+$ref must produce a fully
+    resolved Pydantic model (regression test for _get_combined_attributes omitting
+    additionalProperties from schema traversal).
+    """
+    api = OpenAPI("/", with_schema_additionalProperties_nullable_allof)
+
+    for op in ["implicit-allOf", "explicit-allOf", "explicit-oneOf"]:
+        schema = api._[op].return_value()
+        value_type = schema.additionalProperties.get_type()
+
+        assert value_type.__pydantic_complete__ is True
+
+        # map model accepts null values for the map entries
+        map_type = schema.get_type()
+        result = map_type.model_validate({"obj": {"a": "ABC"}, "none": None})
+        assert result.root["none"] is None
+        assert result.root["obj"].root.a == "ABC"
+
+
 def test_schema_with_patternProperties(with_schema_patternProperties):
     api = OpenAPI("/", with_schema_patternProperties)
     A = api.components.schemas["A"].get_type()