diff --git a/src/vcpkg/build.cpp b/src/vcpkg/build.cpp
index b88a6aef48..60382d5aad 100644
--- a/src/vcpkg/build.cpp
+++ b/src/vcpkg/build.cpp
@@ -765,7 +765,7 @@ namespace vcpkg::Build
             {"_VCPKG_DOWNLOAD_TOOL", to_string(action.build_options.download_tool)},
             {"_VCPKG_EDITABLE", Util::Enum::to_bool(action.build_options.editable) ? "1" : "0"},
             {"_VCPKG_NO_DOWNLOADS", !Util::Enum::to_bool(action.build_options.allow_downloads) ? "1" : "0"},
-            {"VCPKG_CHAINLOAD_TOOLCHAIN_FILE", action.pre_build_info(VCPKG_LINE_INFO).toolchain_file()},
+            {"Z_VCPKG_CHAINLOAD_TOOLCHAIN_FILE", action.pre_build_info(VCPKG_LINE_INFO).toolchain_file()},
         };
 
         if (action.build_options.download_tool == DownloadTool::ARIA2)