diff --git a/README.md b/README.md
index a402813..4150b3e 100644
--- a/README.md
+++ b/README.md
@@ -475,7 +475,7 @@ cd vscode && npm install && npm run esbuild  # VS Code extension
 npx @vscode/vsce package                     # VSIX
 ```
 
-Requires Rust stable, Node.js 18+, VS Code 1.90+.
+Requires rustup (it installs the Rust version pinned in `rust-toolchain.toml`), Node.js 18+, VS Code 1.90+.
 
 ---
 
diff --git a/rust-toolchain.toml b/rust-toolchain.toml
new file mode 100644
index 0000000..7eaaa41
--- /dev/null
+++ b/rust-toolchain.toml
@@ -0,0 +1,10 @@
+# One compiler for every release build. Each platform's engine is built on a
+# different host (and linux-arm64 in a container that installs Rust itself);
+# without a pin they drifted onto three different rustc versions, so one release
+# shipped binaries the same source compiled differently.
+[toolchain]
+channel = "1.94.1"
+components = ["rustfmt", "clippy"]
+profile = "minimal"
+# darwin-x64 is cross-built on the arm64 Mac.
+targets = ["x86_64-apple-darwin"]
diff --git a/scripts/build-linux-arm64.sh b/scripts/build-linux-arm64.sh
index a66e395..6b85005 100755
--- a/scripts/build-linux-arm64.sh
+++ b/scripts/build-linux-arm64.sh
@@ -139,7 +139,7 @@ apt_install gcc-11 g++-11 clang libclang-dev cmake pkg-config libssl-dev make bi
 
 if ! command -v cargo >/dev/null 2>&1; then
   curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs \
-    | sh -s -- -y --default-toolchain stable --profile minimal >/dev/null || exit 1
+    | sh -s -- -y --default-toolchain none --profile minimal >/dev/null || exit 1
 fi
 . "$HOME/.cargo/env"
 
@@ -162,6 +162,7 @@ restore_ownership() {
 trap restore_ownership EXIT
 
 cd /src
+rustc --version || { echo "RUST TOOLCHAIN INSTALL FAILED"; exit 1; }
 export CARGO_TARGET_DIR=/target
 export CC=gcc-11 CXX=g++-11
 export CARGO_TARGET_AARCH64_UNKNOWN_LINUX_GNU_LINKER=gcc-11
diff --git a/vscode/README.md b/vscode/README.md
index c88bb82..a960c3a 100644
--- a/vscode/README.md
+++ b/vscode/README.md
@@ -145,7 +145,7 @@ cd vscode && npm install && npm run esbuild  # VS Code extension
 npx @vscode/vsce package                     # VSIX
 ```
 
-Requires Rust stable, Node.js 18+, VS Code 1.90+.
+Requires rustup (it installs the Rust version pinned in `rust-toolchain.toml`), Node.js 18+, VS Code 1.90+.
 
 ---