diff --git a/src/GZipEncoder.h b/src/GZipEncoder.h
index 4ba83ac2..8f7f3057 100644
--- a/src/GZipEncoder.h
+++ b/src/GZipEncoder.h
@@ -52,6 +52,8 @@ private:
   std::string internalBuf_;
 
   std::string encode(const unsigned char* in, size_t length, int flush);
+  // Not implemented
+  GZipEncoder& operator<<(char c);
 public:
   GZipEncoder();