diff --git a/src/fastmcp/utilities/openapi/director.py b/src/fastmcp/utilities/openapi/director.py
index c3225af92..b0b29f0ba 100644
--- a/src/fastmcp/utilities/openapi/director.py
+++ b/src/fastmcp/utilities/openapi/director.py
@@ -75,14 +75,19 @@ class RequestDirector:
         json_body: dict[str, Any] | list[Any] | None = None
         content: str | bytes | None = None
 
-        # Step 5: Determine the declared content type from the OpenAPI spec
+        # Step 5: Determine the declared content type from the OpenAPI spec.
+        # Strip parameters (e.g. "; charset=utf-8") for dispatch matching.
         declared_content_type: str | None = None
         if route.request_body and route.request_body.content_schema:
-            declared_content_type = next(iter(route.request_body.content_schema))
+            raw_ct = next(iter(route.request_body.content_schema))
+            declared_content_type = raw_ct.split(";")[0].strip().lower()
 
-        # httpx requires cookie values to be strings
+        # httpx requires cookie values to be strings; use OpenAPI-style
+        # serialization (e.g. true/false for booleans, not True/False)
         cookies = (
-            {k: str(v) for k, v in cookie_params.items()} if cookie_params else None
+            {k: _query_scalar_to_str(v) for k, v in cookie_params.items()}
+            if cookie_params
+            else None
         )
 
         # Step 6: Handle request body — dispatch on declared content type.
diff --git a/tests/utilities/openapi/test_director.py b/tests/utilities/openapi/test_director.py
index 82035a79c..acd50425f 100644
--- a/tests/utilities/openapi/test_director.py
+++ b/tests/utilities/openapi/test_director.py
@@ -1403,7 +1403,7 @@ class TestCookieParameters:
         assert "xyz789" in request.headers.get("cookie", "")
 
     def test_cookie_non_string_value_stringified(self, director):
-        """Non-string cookie values (e.g. int) must be stringified for httpx."""
+        """Non-string cookie values (e.g. int, bool) use OpenAPI serialization."""
         route = HTTPRoute(
             path="/api",
             method="GET",
@@ -1415,11 +1415,20 @@ class TestCookieParameters:
                     required=True,
                     schema={"type": "integer"},
                 ),
+                ParameterInfo(
+                    name="debug",
+                    location="cookie",
+                    required=False,
+                    schema={"type": "boolean"},
+                ),
             ],
             parameter_map={
                 "version": {"location": "cookie", "openapi_name": "version"},
+                "debug": {"location": "cookie", "openapi_name": "debug"},
             },
         )
-        request = director.build(route, {"version": 3})
-        assert "version" in request.headers.get("cookie", "")
-        assert "3" in request.headers.get("cookie", "")
+        request = director.build(route, {"version": 3, "debug": True})
+        cookie = request.headers.get("cookie", "")
+        assert "version=3" in cookie
+        # Booleans use OpenAPI convention (true/false, not True/False)
+        assert "debug=true" in cookie