diff --git a/CMakeLists.txt b/CMakeLists.txt
index 7d5e06ea8f..3897dcc074 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -201,8 +201,12 @@ if(WIN32)
 
   set(CURL_TARGET_WINDOWS_VERSION "" CACHE STRING "Minimum target Windows version as hex string")
   if(CURL_TARGET_WINDOWS_VERSION)
-    set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS "_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
-    list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")  # Apply to all feature checks
+    if(CURL_TARGET_WINDOWS_VERSION MATCHES "^0x[0-9a-fA-F]+$")
+      set_property(DIRECTORY APPEND PROPERTY COMPILE_DEFINITIONS "_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")
+      list(APPEND CMAKE_REQUIRED_DEFINITIONS "-D_WIN32_WINNT=${CURL_TARGET_WINDOWS_VERSION}")  # Apply to all feature checks
+    else()
+      message(WARNING "CURL_TARGET_WINDOWS_VERSION value '${CURL_TARGET_WINDOWS_VERSION}' is not a valid hex string.")
+    endif()
   endif()
 
   # Detect actual value of _WIN32_WINNT and store as HAVE_WIN32_WINNT
diff --git a/docs/INSTALL-CMAKE.md b/docs/INSTALL-CMAKE.md
index b6d51da508..eed6218350 100644
--- a/docs/INSTALL-CMAKE.md
+++ b/docs/INSTALL-CMAKE.md
@@ -249,7 +249,7 @@ target_link_libraries(my_target PRIVATE CURL::libcurl)
 - `CURL_LTO`:                               Enable compiler Link Time Optimizations. Default: `OFF`
 - `CURL_PATCHSTAMP`:                        Set security patch string for `curl -V`/`curl --version` output.
 - `CURL_STATIC_CRT`:                        Build libcurl with static CRT with MSVC (`/MT`) (requires UCRT, static libcurl or no curl executable). Default: `OFF`
-- `CURL_TARGET_WINDOWS_VERSION`:            Minimum target Windows version as hex string.
+- `CURL_TARGET_WINDOWS_VERSION`:            Minimum target Windows version as hex string, e.g. `0x0a00` for Windows 10.
 - `CURL_WERROR`:                            Turn compiler warnings into errors. Default: `OFF`
 - `ENABLE_CURL_MANUAL`:                     Build the man page for curl and enable its `-M`/`--manual` option. Default: `ON`
 - `ENABLE_DEBUG`:                           Enable curl debug features (for developing curl itself). Default: `OFF`