@@ -17,6 +17,11 @@ env:
   # The Pyodide release to build for. Its Python version, Emscripten version,
   # and Rust toolchain all come from this release's cross-build environment.
   PYODIDE_VERSION: "314.0.7"
+  # The oldest Rust that compiles our dependencies. DataFusion 55 needs 1.94,
+  # newer than Pyodide 314.0.7's 1.93.0, so the build uses whichever of the
+  # two is newer. Both are stable releases; the smoke test below loads the
+  # wheel in Pyodide, which catches a toolchain Pyodide can't load.
+  MIN_RUST_TOOLCHAIN: "1.94.0"
 
 jobs:
   build:
@@ -34,7 +39,10 @@ jobs:
         run: |
           pip install pyodide-build
           pyodide xbuildenv install "$PYODIDE_VERSION"
-          echo "RUST_TOOLCHAIN=$(pyodide config get rust_toolchain)" >> "$GITHUB_ENV"
+          PYODIDE_RUST="$(pyodide config get rust_toolchain)"
+          RUST_TOOLCHAIN="$(printf '%s\n' "$PYODIDE_RUST" "$MIN_RUST_TOOLCHAIN" | sort -V | tail -n 1)"
+          echo "Pyodide's Rust: $PYODIDE_RUST; building with: $RUST_TOOLCHAIN"
+          echo "RUST_TOOLCHAIN=$RUST_TOOLCHAIN" >> "$GITHUB_ENV"
 
       - name: Install Rust
         uses: dtolnay/rust-toolchain@master