diff --git a/examples/book_client/book_client.cc b/examples/book_client/book_client.cc
index 2531a20..7e779a8 100644
--- a/examples/book_client/book_client.cc
+++ b/examples/book_client/book_client.cc
@@ -10,9 +10,8 @@
 
 BookClient::BookClient(const std::string& url, int timeout)
     : url_(url), session_(timeout) {
-  // Default Content-Type for requests who have a body.
-  session_.set_media_type("application/json");
-  session_.set_charset("utf-8");
+  // Default Content-Type for requests with a body.
+  session_.SetContentType("application/json", "utf-8");
 }
 
 bool BookClient::Query(std::list<Book>* books) {
diff --git a/webcc/client_session.h b/webcc/client_session.h
index 04bfcd0..8e28baa 100644
--- a/webcc/client_session.h
+++ b/webcc/client_session.h
@@ -38,11 +38,13 @@ public:
     headers_.Set(key, value);
   }
 
-  void set_media_type(const std::string& media_type) {
+  // Set `Content-Type` header, e.g., ("application/json", "utf-8").
+  // Only applied when:
+  //   - the request to send has no `Content-Type` header, and
+  //   - the request has a body.
+  void SetContentType(const std::string& media_type,
+                      const std::string& charset = "") {
     media_type_ = media_type;
-  }
-
-  void set_charset(const std::string& charset) {
     charset_ = charset;
   }