diff --git a/include/connection.hpp b/include/connection.hpp
index c6d557c..67bc6f1 100644
--- a/include/connection.hpp
+++ b/include/connection.hpp
@@ -85,7 +85,7 @@ public:
      *
      *  @since  0.1.0
      */
-    explicit Connection(Instance &instance)
+    explicit Connection(const Instance &instance)
         : _instance{instance}
         , _baseuri{instance.get_baseuri()}
     {
@@ -292,7 +292,7 @@ public:
         CURLWrapper::cancel_stream();
     }
 private:
-    Instance &_instance;
+    const Instance &_instance;
     const string_view _baseuri;
 
     [[nodiscard]]
diff --git a/include/instance.hpp b/include/instance.hpp
index 1997068..fb85a03 100644
--- a/include/instance.hpp
+++ b/include/instance.hpp
@@ -94,7 +94,7 @@ public:
      *
      *  @since  0.3.0
      */
-    inline void copy_connection_properties(CURLWrapper &curlwrapper)
+    inline void copy_connection_properties(CURLWrapper &curlwrapper) const
     {
         curlwrapper.setup_connection_properties(_proxy, _access_token, _cainfo,
                                                 _useragent);