diff --git a/connexion/utils.py b/connexion/utils.py
index 5458ca85b..f97567b4d 100644
--- a/connexion/utils.py
+++ b/connexion/utils.py
@@ -158,7 +158,7 @@ def is_json_mimetype(mimetype):
     if mimetype is None:
         return False
 
-    maintype, subtype = mimetype.split("/")  # type: str, str
+    maintype, subtype = mimetype.split("/", maxsplit=1)  # type: str, str
     if ";" in subtype:
         subtype, parameter = subtype.split(";", maxsplit=1)
     return maintype == "application" and (
@@ -310,10 +310,8 @@ def extract_content_type(
 
         if decoded_key.lower() == "content-type":
             if isinstance(value, bytes):
-                content_type = value.decode("latin-1")
-            else:
-                content_type = value
-            break
+                value = value.decode("latin-1")
+            content_type = ",".join([content_type, value] if content_type else [value])
 
     return content_type
 
diff --git a/tests/test_json_validation.py b/tests/test_json_validation.py
index aa9b0cf30..a51685450 100644
--- a/tests/test_json_validation.py
+++ b/tests/test_json_validation.py
@@ -175,3 +175,26 @@ class MyDefaultsJSONBodyValidator(DefaultsJSONRequestBodyValidator):
     )
     assert res.status_code == 200
     assert res.json().get("human")
+
+
+def test_multiple_json_content_type(json_validation_spec_dir, spec):
+    """ensure that defaults applied that modify the body"""
+
+    class MyDefaultsJSONBodyValidator(DefaultsJSONRequestBodyValidator):
+        pass
+
+    validator_map = {"body": {"application/json": MyDefaultsJSONBodyValidator}}
+
+    app = App(__name__, specification_dir=json_validation_spec_dir)
+    app.add_api(spec, validate_responses=True, validator_map=validator_map)
+    app_client = app.test_client()
+
+    res = app_client.post(
+        "/v1.0/user",
+        data=json.dumps({"name": "foo"}),
+        headers={
+            "content-type": "application/json",
+            "Content-Type": "application/json",
+        },
+    )
+    assert res.status_code == 415
diff --git a/tests/test_utils.py b/tests/test_utils.py
index adfa1b115..26a8763bd 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -62,16 +62,29 @@ def test_deep_get_list():
     assert utils.deep_get(obj, ["0", "properties", "id"]) == {"type": "string"}
 
 
-def test_is_json_mimetype():
-    assert utils.is_json_mimetype("application/json")
-    assert utils.is_json_mimetype("application/vnd.com.myEntreprise.v6+json")
-    assert utils.is_json_mimetype(
-        "application/vnd.scanner.adapter.vuln.report.harbor+json; version=1.0"
-    )
-    assert utils.is_json_mimetype(
-        "application/vnd.com.myEntreprise.v6+json; charset=UTF-8"
-    )
-    assert not utils.is_json_mimetype("text/html")
+@pytest.mark.parametrize(
+    "mime_type",
+    [
+        "application/json",
+        "application/vnd.com.myEntreprise.v6+json",
+        "application/vnd.scanner.adapter.vuln.report.harbor+json; version=1.0",
+        "application/vnd.com.myEntreprise.v6+json; charset=UTF-8",
+    ],
+)
+def test_is_json_mimetype_true(mime_type: str):
+    assert utils.is_json_mimetype(mime_type)
+
+
+@pytest.mark.parametrize(
+    "mime_type",
+    [
+        "application/json,application/json",
+        "text/html",
+        "text/json",
+    ],
+)
+def test_is_json_mimetype_false(mime_type: str):
+    assert not utils.is_json_mimetype(mime_type)
 
 
 def test_sort_routes():