diff --git a/chat_messages.hpp b/chat_messages.hpp
index 7686304..8664356 100644
--- a/chat_messages.hpp
+++ b/chat_messages.hpp
@@ -37,7 +37,7 @@ namespace chat
         { return sizeof(char) + _content.size() + sizeof(char); }
     };
 
-    std::ostream& operator<<(std::ostream& os, const chat_message& msg)
+    inline std::ostream& operator<<(std::ostream& os, const chat_message& msg)
     { return os << msg.get(); }
 }