diff --git a/README.md b/README.md
index d4e1820..48ce645 100644
--- a/README.md
+++ b/README.md
@@ -63,6 +63,8 @@ Ubuntu-to-Windows `Setup.exe` build:
 
 ```bash
 cd desktop-client
+sudo apt update
+sudo apt install -y clang lld llvm nsis
 cargo install --locked cargo-xwin
 rustup target add x86_64-pc-windows-msvc
 npm install
diff --git a/desktop-client/scripts/cargo-xwin b/desktop-client/scripts/cargo-xwin
index d744160..0640353 100644
--- a/desktop-client/scripts/cargo-xwin
+++ b/desktop-client/scripts/cargo-xwin
@@ -1,4 +1,12 @@
 #!/usr/bin/env bash
 set -eu
 
+if ! command -v clang-cl >/dev/null 2>&1; then
+  echo "clang-cl is required for Windows cross-builds on Linux."
+  echo "Install LLVM/Clang toolchain first, for example on Ubuntu:"
+  echo "  sudo apt update"
+  echo "  sudo apt install -y clang lld llvm"
+  exit 1
+fi
+
 exec cargo xwin "$@"