diff --git a/cmake/hex.cmake b/cmake/hex.cmake
index c3935f613f..f5eb586f7b 100644
--- a/cmake/hex.cmake
+++ b/cmake/hex.cmake
@@ -1,5 +1,9 @@
 # SPDX-License-Identifier: Apache-2.0
 
+# This code was deprecated after Zephyr v3.5.0
+message(DEPRECATION "The to_hex() and from_hex() functions are deprecated. Please "
+                    "use CMake's math(... OUTPUT_FORMAT <format>) instead.")
+
 # from https://gist.github.com/korzo89/71a6de0f388f7cf8b349101b0134060c
 function(from_hex HEX DEC)
     string(SUBSTRING "${HEX}" 2 -1 HEX)