diff --git a/buffet/transport_interface.h b/buffet/transport_interface.h
index 0f9363b..e833239 100644
--- a/buffet/transport_interface.h
+++ b/buffet/transport_interface.h
@@ -37,26 +37,26 @@
   virtual void AddRange(int64_t bytes) = 0;
   virtual void AddRange(uint64_t from_byte, uint64_t to_byte) = 0;
 
-  virtual void SetAccept(char const* accept_mime_types) = 0;
+  virtual void SetAccept(const char* accept_mime_types) = 0;
   virtual std::string GetAccept() const = 0;
 
   virtual std::string GetRequestURL() const = 0;
 
-  virtual void SetContentType(char const* content_type) = 0;
+  virtual void SetContentType(const char* content_type) = 0;
   virtual std::string GetContentType() const = 0;
 
-  virtual void AddHeader(char const* header, char const* value) = 0;
-  virtual void RemoveHeader(char const* header) = 0;
+  virtual void AddHeader(const char* header, const char* value) = 0;
+  virtual void RemoveHeader(const char* header) = 0;
 
-  virtual bool AddRequestBody(void const* data, size_t size) = 0;
+  virtual bool AddRequestBody(const void* data, size_t size) = 0;
 
-  virtual void SetMethod(char const* method) = 0;
+  virtual void SetMethod(const char* method) = 0;
   virtual std::string GetMethod() const = 0;
 
-  virtual void SetReferer(char const* referer) = 0;
+  virtual void SetReferer(const char* referer) = 0;
   virtual std::string GetReferer() const = 0;
 
-  virtual void SetUserAgent(char const* user_agent) = 0;
+  virtual void SetUserAgent(const char* user_agent) = 0;
   virtual std::string GetUserAgent() const = 0;
 
   virtual bool Perform() = 0;
@@ -64,8 +64,8 @@
   virtual int GetResponseStatusCode() const = 0;
   virtual std::string GetResponseStatusText() const = 0;
 
-  virtual std::string GetResponseHeader(char const* header_name) const = 0;
-  virtual std::vector<unsigned char> const& GetResponseData() const = 0;
+  virtual std::string GetResponseHeader(const char* header_name) const = 0;
+  virtual const std::vector<unsigned char>& GetResponseData() const = 0;
   virtual std::string GetErrorMessage() const = 0;
 
   virtual void Close() = 0;