diff --git a/CHANGELOG.md b/CHANGELOG.md
index 6904aea..438db2b 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ options. The project adheres to semantic versioning.
 
 * Fix a warning about possible loss of data.
 * Fix version numbering in CMakeLists.txt
+* Remove unused declaration of the undefined `ParseResult::get_option`.
 
 ## 2.1.1
 
diff --git a/include/cxxopts.hpp b/include/cxxopts.hpp
index b6865d9..562bef3 100644
--- a/include/cxxopts.hpp
+++ b/include/cxxopts.hpp
@@ -1143,9 +1143,6 @@ namespace cxxopts
 
     private:
 
-    OptionValue&
-    get_option(std::shared_ptr<OptionDetails>);
-
     void
     parse(int& argc, char**& argv);