diff --git a/src/tiffcomposite_int.hpp b/src/tiffcomposite_int.hpp
index aa4d860f..532c01b0 100644
--- a/src/tiffcomposite_int.hpp
+++ b/src/tiffcomposite_int.hpp
@@ -397,7 +397,9 @@ namespace Exiv2 {
     //! Search key for TIFF mapping structures.
     struct TiffMappingInfo::Key {
         //! Constructor
-        Key(const std::string& m, uint32_t e, IfdId g) : m_(m), e_(e), g_(g) {}
+        Key(std::string m, uint32_t e, IfdId g) : m_(std::move(m)), e_(e), g_(g)
+        {
+        }
         std::string m_;                    //!< Camera make
         uint32_t    e_;                    //!< Extended tag
         IfdId       g_;                    //!< %Group