diff --git a/crates/uv-python/src/downloads.rs b/crates/uv-python/src/downloads.rs
index 1975a5a49dd..3cadf420c09 100644
--- a/crates/uv-python/src/downloads.rs
+++ b/crates/uv-python/src/downloads.rs
@@ -455,6 +455,11 @@ impl PythonDownloadRequest {
         self.implementation.as_ref()
     }
 
+    /// Return the requested build, if any.
+    pub fn build(&self) -> Option<&str> {
+        self.build.as_deref()
+    }
+
     pub(crate) fn version(&self) -> Option<&VersionRequest> {
         self.version.as_ref()
     }
diff --git a/crates/uv/src/commands/python/install.rs b/crates/uv/src/commands/python/install.rs
index 4c4704f9f70..3f6bad393a0 100644
--- a/crates/uv/src/commands/python/install.rs
+++ b/crates/uv/src/commands/python/install.rs
@@ -554,10 +554,19 @@ async fn perform_install(
                 }
             } else if let Some(installation) = existing_installations
                 .iter()
-                .find(|inst| request.matches_installation(inst))
+                .find(|inst| request.download_request.satisfied_by_key(inst.key()))
             {
-                debug!("Found `{}` for request `{}`", installation.key(), request);
-                satisfied.push(installation);
+                if matches_build(request.download_request.build(), installation.build()) {
+                    debug!("Found `{}` for request `{}`", installation.key(), request);
+                    satisfied.push(installation);
+                } else {
+                    debug!(
+                        "Build version mismatch for `{}`, will reinstall",
+                        installation.key()
+                    );
+                    changelog.existing.insert(installation.key().clone());
+                    unsatisfied.push(Cow::Borrowed(request));
+                }
             } else {
                 debug!("No installation found for request `{}`", request);
                 unsatisfied.push(Cow::Borrowed(request));
@@ -609,6 +618,10 @@ async fn perform_install(
 
     let mut tasks = futures::stream::iter(&downloads)
         .map(async |download| {
+            let reinstall = reinstall
+                || existing_installations
+                    .iter()
+                    .any(|installation| download.key() == installation.key());
             (
                 *download,
                 download
diff --git a/crates/uv/tests/python/python_install.rs b/crates/uv/tests/python/python_install.rs
index b0e502738a1..c268579d000 100644
--- a/crates/uv/tests/python/python_install.rs
+++ b/crates/uv/tests/python/python_install.rs
@@ -4110,6 +4110,29 @@ fn python_install_build_version() {
     let build_content = fs_err::read_to_string(&build_file_path).unwrap();
     assert_eq!(build_content, "20240814");
 
+    // A matching patch with an outdated build must be re-extracted for an explicit build pin.
+    let stale_file = cpython_dir.child("stale-file");
+    stale_file.touch().unwrap();
+    fs_err::write(&build_file_path, "19000101").unwrap();
+
+    uv_snapshot!(context.filters(), context.python_install()
+        .arg("3.12.5")
+        .env(EnvVars::UV_PYTHON_CPYTHON_BUILD, "20240814"), @"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Installed Python 3.12.5 in [TIME]
+     ~ cpython-3.12.5-[PLATFORM]
+    ");
+
+    assert!(!stale_file.exists());
+    assert_eq!(
+        fs_err::read_to_string(&build_file_path).unwrap(),
+        "20240814"
+    );
+
     // We should find the build
     uv_snapshot!(context.filters(), context.python_find()
         .arg("3.12")