diff --git a/tl_expected/include/tl_expected/expected.hpp b/tl_expected/include/tl_expected/expected.hpp
index ae90975..9a2c653 100644
--- a/tl_expected/include/tl_expected/expected.hpp
+++ b/tl_expected/include/tl_expected/expected.hpp
@@ -16,6 +16,9 @@
 #ifndef TL_EXPECTED_HPP
 #define TL_EXPECTED_HPP
 
+#warning "tl_expected/expected.hpp is deprecated and will be removed by the ROS 2 Lyrical Luth release. \
+  Use <tl/expected.hpp> from libexpected-dev, or <rcpputils/tl_expected/expected.hpp> if the system header is not available."
+
 #define TL_EXPECTED_VERSION_MAJOR 1
 #define TL_EXPECTED_VERSION_MINOR 2
 #define TL_EXPECTED_VERSION_PATCH 0