diff --git a/crates/uv-build/src/lib.rs b/crates/uv-build/src/lib.rs
index dcda79cf6992..c162e086f919 100644
--- a/crates/uv-build/src/lib.rs
+++ b/crates/uv-build/src/lib.rs
@@ -437,38 +437,22 @@ impl SourceBuild {
         let package_name = project.clone().map(|p| p.name);
 
         // Create a virtual environment, or install into the shared environment if requested.
-        let venv = match build_isolation {
-            BuildIsolation::Isolated => uv_virtualenv::create_venv(
+        let venv = if let Some(venv) =  build_isolation.shared_environment(package_name.as_ref()) {
+            venv.clone()
+        } else {
+            uv_virtualenv::create_venv(
                 temp_dir.path(),
                 interpreter.clone(),
                 uv_virtualenv::Prompt::None,
                 false,
                 false,
                 false,
-            )?,
-            BuildIsolation::Shared(venv) => venv.clone(),
-            BuildIsolation::SharedPackage(venv, packages) => {
-                if package_name
-                    .as_ref()
-                    .is_some_and(|name| packages.iter().any(|p| p == name))
-                {
-                    venv.clone()
-                } else {
-                    uv_virtualenv::create_venv(
-                        temp_dir.path(),
-                        interpreter.clone(),
-                        uv_virtualenv::Prompt::None,
-                        false,
-                        false,
-                        false,
-                    )?
-                }
-            }
+            )?
         };
 
         // Setup the build environment. If build isolation is disabled, we assume the build
         // environment is already setup.
-        if build_isolation.is_isolated(&package_name) {
+        if build_isolation.is_isolated(package_name.as_ref()) {
             let resolved_requirements = Self::get_resolved_requirements(
                 build_context,
                 source_build_context,
@@ -518,7 +502,7 @@ impl SourceBuild {
         // Create the PEP 517 build environment. If build isolation is disabled, we assume the build
         // environment is already setup.
         let runner = PythonRunner::new(concurrent_builds);
-        if build_isolation.is_isolated(&package_name) {
+        if build_isolation.is_isolated(package_name.as_ref()) {
             if let Some(pep517_backend) = &pep517_backend {
                 create_pep517_build_environment(
                     &runner,
diff --git a/crates/uv-types/src/builds.rs b/crates/uv-types/src/builds.rs
index dda14b4ee790..deca2b4a0c83 100644
--- a/crates/uv-types/src/builds.rs
+++ b/crates/uv-types/src/builds.rs
@@ -11,14 +11,28 @@ pub enum BuildIsolation<'a> {
 }
 
 impl<'a> BuildIsolation<'a> {
-    /// Returns `true` if build isolation is enforced.
-    pub fn is_isolated(&self, package_name: &Option<PackageName>) -> bool {
+    /// Returns `true` if build isolation is enforced for the given package name.
+    pub fn is_isolated(&self, package: Option<&PackageName>) -> bool {
         match self {
             Self::Isolated => true,
             Self::Shared(_) => false,
-            Self::SharedPackage(_, packages) => match package_name {
-                Some(package_name) => !packages.iter().any(|p| p == package_name),
-                None => true,
+            Self::SharedPackage(_, packages) => package.map_or(true, |package| {
+                !packages.iter().any(|p| p == package)
+            }),
+        }
+    }
+
+    /// Returns the shared environment for a given package, if build isolation is not enforced.
+    pub fn shared_environment(&self, package: Option<&PackageName>) -> Option<&PythonEnvironment> {
+        match self {
+            Self::Isolated => None,
+            Self::Shared(env) => Some(env),
+            Self::SharedPackage(env, packages) => if package.is_some_and(|package| {
+                packages.iter().any(|p| p == package)
+            }) {
+                Some(env)
+            } else {
+                None
             },
         }
     }