diff --git a/resend/async_request.py b/resend/async_request.py
index c647ac9..344d190 100644
--- a/resend/async_request.py
+++ b/resend/async_request.py
@@ -155,7 +155,7 @@ async def make_request(self, url: str) -> Union[Dict[str, Any], List[Any]]:
             "content-type", ""
         )
 
-        if "application/json" not in content_type:
+        if content_type.split(";", 1)[0].strip().lower() != "application/json":
             raise_for_code_and_type(
                 code=error_code,
                 message=f"Expected JSON response but got: {content_type}",
diff --git a/resend/request.py b/resend/request.py
index 56d27c1..8d4c8de 100644
--- a/resend/request.py
+++ b/resend/request.py
@@ -140,7 +140,7 @@ def make_request(self, url: str) -> Union[Dict[str, Any], List[Any]]:
             "content-type", ""
         )
 
-        if "application/json" not in content_type:
+        if content_type.split(";", 1)[0].strip().lower() != "application/json":
             raise_for_code_and_type(
                 code=error_code,
                 message=f"Expected JSON response but got: {content_type}",
diff --git a/tests/content_type_test.py b/tests/content_type_test.py
new file mode 100644
index 0000000..057f760
--- /dev/null
+++ b/tests/content_type_test.py
@@ -0,0 +1,82 @@
+import asyncio
+from typing import Any, Dict
+from unittest.mock import AsyncMock, Mock, patch
+
+import pytest
+
+from resend.async_request import AsyncRequest
+from resend.exceptions import RateLimitError, ResendError
+from resend.request import Request
+
+
+def _perform_request(
+    use_async: bool, content: bytes, status_code: int, headers: Dict[str, str]
+) -> Dict[str, Any]:
+    if use_async:
+        async_client = AsyncMock()
+        async_client.request.return_value = (content, status_code, headers)
+        with patch("resend.default_async_http_client", async_client):
+            req = AsyncRequest[Dict[str, Any]]("/emails", {}, "get")
+            return asyncio.run(req.perform_with_content())
+
+    sync_client = Mock()
+    sync_client.request.return_value = (content, status_code, headers)
+    with patch("resend.default_http_client", sync_client):
+        return Request[Dict[str, Any]]("/emails", {}, "get").perform_with_content()
+
+
+@pytest.mark.parametrize("use_async", [False, True], ids=["sync", "async"])
+@pytest.mark.parametrize("header_name", ["content-type", "Content-Type"])
+@pytest.mark.parametrize(
+    "content_type",
+    [
+        "application/json",
+        "application/json; charset=utf-8",
+        "Application/JSON",
+        "APPLICATION/JSON; CHARSET=UTF-8",
+        " application/json ; charset=utf-8 ",
+    ],
+)
+class TestJsonContentType:
+    def test_json_content_type_is_accepted(
+        self, use_async: bool, header_name: str, content_type: str
+    ) -> None:
+        headers = {header_name: content_type}
+        response = _perform_request(use_async, b'{"id":"email_123"}', 200, headers)
+
+        assert response["id"] == "email_123"
+        assert response["http_headers"] == headers
+
+    def test_json_error_preserves_error_type_and_headers(
+        self, use_async: bool, header_name: str, content_type: str
+    ) -> None:
+        headers = {header_name: content_type, "retry-after": "2"}
+        content = b'{"name":"rate_limit_exceeded","message":"Too many requests"}'
+
+        with pytest.raises(RateLimitError) as error:
+            _perform_request(use_async, content, 429, headers)
+
+        assert error.value.code == 429
+        assert error.value.error_type == "rate_limit_exceeded"
+        assert error.value.message == "Too many requests"
+        assert error.value.headers == headers
+
+
+@pytest.mark.parametrize("use_async", [False, True], ids=["sync", "async"])
+@pytest.mark.parametrize(
+    "content_type",
+    ["text/plain", "application/jsonp", "text/plain; note=application/json", ""],
+)
+@pytest.mark.parametrize("status_code", [200, 429])
+class TestNonJsonContentType:
+    def test_non_json_content_type_is_rejected(
+        self, use_async: bool, content_type: str, status_code: int
+    ) -> None:
+        headers = {"content-type": content_type, "retry-after": "2"}
+
+        with pytest.raises(ResendError) as error:
+            _perform_request(use_async, b'{"id":"email_123"}', status_code, headers)
+
+        assert error.value.code == (status_code if status_code >= 400 else 500)
+        assert error.value.headers == headers
+        assert error.value.message == f"Expected JSON response but got: {content_type}"