diff --git a/pyproject.toml b/pyproject.toml
index 0de10a2..d971a0d 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -15,6 +15,7 @@ packages = [
 python = "^3.7"
 tornado = "^4 || ^5 || ^6"
 openapi-core = "^0.13.4"
+ietfparse = "^1.7.0"
 
 [tool.poetry.dev-dependencies]
 black = { version = "*", allow-prereleases = true }
diff --git a/tests/test_util.py b/tests/test_util.py
new file mode 100644
index 0000000..d77e08a
--- /dev/null
+++ b/tests/test_util.py
@@ -0,0 +1,16 @@
+import unittest
+
+from tornado_openapi3 import util
+
+
+class TestMimetypeParsing(unittest.TestCase):
+    def test_parameters_are_stripped(self) -> None:
+        self.assertEqual("text/html", util.parse_mimetype("text/html; charset=utf-8"))
+
+    def test_mimetype_is_lowercase(self) -> None:
+        self.assertEqual("text/html", util.parse_mimetype("TEXT/HTML"))
+
+    def test_type_suffix_is_preserved(self) -> None:
+        self.assertEqual(
+            "application/custom+json", util.parse_mimetype("application/custom+json")
+        )
diff --git a/tornado_openapi3/requests.py b/tornado_openapi3/requests.py
index 259f40c..0af3581 100644
--- a/tornado_openapi3/requests.py
+++ b/tornado_openapi3/requests.py
@@ -12,6 +12,8 @@ from tornado.httpclient import HTTPRequest  # type: ignore
 from tornado.httputil import HTTPServerRequest  # type: ignore
 from werkzeug.datastructures import ImmutableMultiDict, Headers
 
+from .util import parse_mimetype
+
 
 class TornadoRequestFactory:
     @classmethod
@@ -44,8 +46,8 @@ class TornadoRequestFactory:
                 query=query_arguments, header=Headers(request.headers.get_all())
             ),
             body=request.body if request.body else b"",
-            mimetype=request.headers.get(
-                "Content-Type", "application/x-www-form-urlencoded"
+            mimetype=parse_mimetype(
+                request.headers.get("Content-Type", "application/x-www-form-urlencoded")
             ),
         )
 
diff --git a/tornado_openapi3/responses.py b/tornado_openapi3/responses.py
index fc87f4a..89365fe 100644
--- a/tornado_openapi3/responses.py
+++ b/tornado_openapi3/responses.py
@@ -6,12 +6,13 @@ from openapi_core.validation.response import validators  # type: ignore
 from tornado.httpclient import HTTPResponse  # type: ignore
 
 from .requests import TornadoRequestFactory
+from .util import parse_mimetype
 
 
 class TornadoResponseFactory:
     @classmethod
     def create(cls, response: HTTPResponse) -> OpenAPIResponse:
-        mimetype = response.headers.get("Content-Type", "text/html")
+        mimetype = parse_mimetype(response.headers.get("Content-Type", "text/html"))
         return OpenAPIResponse(
             data=response.body if response.body else b"",
             status_code=response.code,
diff --git a/tornado_openapi3/util.py b/tornado_openapi3/util.py
new file mode 100644
index 0000000..8d39246
--- /dev/null
+++ b/tornado_openapi3/util.py
@@ -0,0 +1,10 @@
+import ietfparse.headers
+
+
+def parse_mimetype(content_type: str) -> str:
+    parsed = ietfparse.headers.parse_content_type(content_type)
+    return "{}/{}{}".format(
+        parsed.content_type,
+        parsed.content_subtype,
+        "+{}".format(parsed.content_suffix) if parsed.content_suffix else "",
+    )