diff --git a/jupyterhub/apihandlers/base.py b/jupyterhub/apihandlers/base.py
index 6020bfb1..f7a82da3 100644
--- a/jupyterhub/apihandlers/base.py
+++ b/jupyterhub/apihandlers/base.py
@@ -78,14 +78,39 @@ class APIHandler(BaseHandler):
             return False
         return True
 
+    def check_post_content_type(self):
+        """Check request content-type, e.g. for cross-site POST requests
+
+        Cross-site POST via form will include content-type
+        """
+        content_type = self.request.headers.get("Content-Type")
+        if not content_type:
+            # not specified, e.g. from a script
+            return True
+
+        # parse content type for application/json
+        fields = content_type.lower().split(";")
+        if not any(f.lstrip().startswith("application/json") for f in fields):
+            self.log.warning(f"Not allowing POST with content-type: {content_type}")
+            return False
+
+        return True
+
     def get_current_user_cookie(self):
-        """Override get_user_cookie to check Referer header"""
+        """Extend get_user_cookie to add checks for CORS"""
         cookie_user = super().get_current_user_cookie()
-        # check referer only if there is a cookie user,
+        # CORS checks for cookie-authentication
+        # check these only if there is a cookie user,
         # avoiding misleading "Blocking Cross Origin" messages
         # when there's no cookie set anyway.
-        if cookie_user and not self.check_referer():
-            return None
+        if cookie_user:
+            if not self.check_referer():
+                return None
+            if (
+                self.request.method.upper() == 'POST'
+                and not self.check_post_content_type()
+            ):
+                return None
         return cookie_user
 
     def get_json_body(self):
diff --git a/jupyterhub/tests/test_api.py b/jupyterhub/tests/test_api.py
index d2d680d6..bbbb7f3f 100644
--- a/jupyterhub/tests/test_api.py
+++ b/jupyterhub/tests/test_api.py
@@ -65,7 +65,7 @@ async def test_auth_api(app):
     assert r.status_code == 403
 
 
-async def test_referer_check(app):
+async def test_cors_checks(app):
     url = ujoin(public_host(app), app.hub.base_url)
     host = urlparse(url).netloc
     # add admin user
@@ -110,6 +110,32 @@ async def test_referer_check(app):
     )
     assert r.status_code == 200
 
+    r = await api_request(
+        app,
+        'users',
+        method='post',
+        data='{}',
+        headers={
+            "Authorization": "",
+            "Content-Type": "text/plain",
+        },
+        cookies=cookies,
+    )
+    assert r.status_code == 403
+
+    r = await api_request(
+        app,
+        'users',
+        method='post',
+        data='{}',
+        headers={
+            "Authorization": "",
+            "Content-Type": "application/json; charset=UTF-8",
+        },
+        cookies=cookies,
+    )
+    assert r.status_code == 400  # accepted, but invalid
+
 
 # --------------
 # User API tests