diff --git a/crates/install-wheel-rs/src/wheel.rs b/crates/install-wheel-rs/src/wheel.rs
index 90d6904c4..651c90138 100644
--- a/crates/install-wheel-rs/src/wheel.rs
+++ b/crates/install-wheel-rs/src/wheel.rs
@@ -1,5 +1,5 @@
 use std::collections::HashMap;
-use std::ffi::OsString;
+
 use std::io::{BufRead, BufReader, BufWriter, Cursor, Read, Seek, Write};
 use std::path::{Path, PathBuf};
 use std::process::{Command, ExitStatus, Stdio};
@@ -446,7 +446,9 @@ fn bytecode_compile(
     let py_source_paths: Vec<_> = unpacked_paths
         .into_iter()
         .filter(|path| {
-            site_packages.join(path).is_file() && path.extension() == Some(&OsString::from("py"))
+            path.extension()
+                .is_some_and(|ext| ext.eq_ignore_ascii_case("py"))
+                && site_packages.join(path).is_file()
         })
         .collect();
 
diff --git a/crates/puffin-build/src/lib.rs b/crates/puffin-build/src/lib.rs
index bc8fc1e60..abeba4739 100644
--- a/crates/puffin-build/src/lib.rs
+++ b/crates/puffin-build/src/lib.rs
@@ -284,39 +284,40 @@ impl SourceBuild {
         };
 
         // Check if we have a PEP 517 build backend.
-        let pep517_backend = if source_tree.join("pyproject.toml").is_file() {
-            let pyproject_toml: PyProjectToml =
-                toml::from_str(&fs::read_to_string(source_tree.join("pyproject.toml"))?)
-                    .map_err(Error::InvalidPyprojectToml)?;
-            if let Some(build_system) = pyproject_toml.build_system {
-                Some(Pep517Backend {
-                    // If `build-backend` is missing, inject the legacy setuptools backend, but
-                    // retain the `requires`, to match `pip` and `build`. Note that while PEP 517
-                    // says that in this case we "should revert to the legacy behaviour of running
-                    // `setup.py` (either directly, or by implicitly invoking the
-                    // `setuptools.build_meta:__legacy__` backend)", we found that in practice, only
-                    // the legacy setuptools backend is allowed. See also:
-                    // https://github.com/pypa/build/blob/de5b44b0c28c598524832dff685a98d5a5148c44/src/build/__init__.py#L114-L118
-                    backend: build_system
-                        .build_backend
-                        .unwrap_or_else(|| "setuptools.build_meta:__legacy__".to_string()),
-                    backend_path: build_system.backend_path,
-                    requirements: build_system.requires,
-                })
-            } else {
-                // If a `pyproject.toml` is present, but `[build-system]` is missing, proceed with
-                // a PEP 517 build using the default backend, to match `pip` and `build`.
-                Some(Pep517Backend {
-                    backend: "setuptools.build_meta:__legacy__".to_string(),
-                    backend_path: None,
-                    requirements: vec![
-                        Requirement::from_str("wheel").unwrap(),
-                        Requirement::from_str("setuptools >= 40.8.0").unwrap(),
-                    ],
-                })
+        let pep517_backend = match fs::read_to_string(source_tree.join("pyproject.toml")) {
+            Ok(toml) => {
+                let pyproject_toml: PyProjectToml =
+                    toml::from_str(&toml).map_err(Error::InvalidPyprojectToml)?;
+                if let Some(build_system) = pyproject_toml.build_system {
+                    Some(Pep517Backend {
+                        // If `build-backend` is missing, inject the legacy setuptools backend, but
+                        // retain the `requires`, to match `pip` and `build`. Note that while PEP 517
+                        // says that in this case we "should revert to the legacy behaviour of running
+                        // `setup.py` (either directly, or by implicitly invoking the
+                        // `setuptools.build_meta:__legacy__` backend)", we found that in practice, only
+                        // the legacy setuptools backend is allowed. See also:
+                        // https://github.com/pypa/build/blob/de5b44b0c28c598524832dff685a98d5a5148c44/src/build/__init__.py#L114-L118
+                        backend: build_system
+                            .build_backend
+                            .unwrap_or_else(|| "setuptools.build_meta:__legacy__".to_string()),
+                        backend_path: build_system.backend_path,
+                        requirements: build_system.requires,
+                    })
+                } else {
+                    // If a `pyproject.toml` is present, but `[build-system]` is missing, proceed with
+                    // a PEP 517 build using the default backend, to match `pip` and `build`.
+                    Some(Pep517Backend {
+                        backend: "setuptools.build_meta:__legacy__".to_string(),
+                        backend_path: None,
+                        requirements: vec![
+                            Requirement::from_str("wheel").unwrap(),
+                            Requirement::from_str("setuptools >= 40.8.0").unwrap(),
+                        ],
+                    })
+                }
             }
-        } else {
-            None
+            Err(err) if err.kind() == io::ErrorKind::NotFound => None,
+            Err(err) => return Err(err.into()),
         };
 
         let venv = gourgeist::create_venv(&temp_dir.path().join(".venv"), interpreter.clone())?;