diff --git a/crates/uv/src/commands/project/install_target.rs b/crates/uv/src/commands/project/install_target.rs
index b9432e1ed5b8..95980ea31880 100644
--- a/crates/uv/src/commands/project/install_target.rs
+++ b/crates/uv/src/commands/project/install_target.rs
@@ -2,7 +2,8 @@ use std::borrow::Cow;
 use std::path::Path;
 use std::str::FromStr;
 
-use itertools::{Either, Itertools};
+use itertools::Either;
+use rustc_hash::FxHashSet;
 
 use uv_configuration::ExtrasSpecification;
 use uv_distribution_types::Index;
@@ -258,10 +259,11 @@ impl<'lock> InstallTarget<'lock> {
             Self::Project { lock, .. }
             | Self::Workspace { lock, .. }
             | Self::NonProjectWorkspace { lock, .. } => {
+                let roots = self.roots().collect::<FxHashSet<_>>();
                 let member_packages: Vec<&Package> = lock
                     .packages()
                     .iter()
-                    .filter(|package| self.roots().contains(package.name()))
+                    .filter(|package| roots.contains(package.name()))
                     .collect();
 
                 // If `provides-extra` is not set in any package, do not perform the check, as this
@@ -274,12 +276,14 @@ impl<'lock> InstallTarget<'lock> {
                     return Ok(());
                 }
 
+                // Collect all known extras from the member packages.
+                let known_extras = member_packages
+                    .iter()
+                    .flat_map(|package| package.provides_extras().into_iter().flatten())
+                    .collect::<FxHashSet<_>>();
+
                 for extra in extras {
-                    if !member_packages.iter().any(|package| {
-                        package
-                            .provides_extras()
-                            .is_some_and(|provides_extras| provides_extras.contains(extra))
-                    }) {
+                    if !known_extras.contains(extra) {
                         return match self {
                             Self::Project { .. } => {
                                 Err(ProjectError::MissingExtraProject(extra.clone()))
diff --git a/crates/uv/tests/it/sync.rs b/crates/uv/tests/it/sync.rs
index de98e2957c91..de933e0ad02b 100644
--- a/crates/uv/tests/it/sync.rs
+++ b/crates/uv/tests/it/sync.rs
@@ -2771,6 +2771,161 @@ fn sync_ignore_extras_check_when_no_provides_extras() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn sync_non_existent_extra_workspace_member() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [project]
+        name = "project"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dependencies = ["child"]
+
+        [project.optional-dependencies]
+        types = ["sniffio>1"]
+
+        [tool.uv.workspace]
+        members = ["child"]
+
+        [tool.uv.sources]
+        child = { workspace = true }
+        "#,
+    )?;
+
+    context
+        .temp_dir
+        .child("child")
+        .child("pyproject.toml")
+        .write_str(
+            r#"
+        [project]
+        name = "child"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+
+        [project.optional-dependencies]
+        async = ["anyio>3"]
+        "#,
+        )?;
+
+    context.lock().assert().success();
+
+    // Requesting an extra that only exists in the child should fail.
+    uv_snapshot!(context.filters(), context.sync().arg("--extra").arg("async"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 5 packages in [TIME]
+    error: Extra `async` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    // Unless we sync from the child directory.
+    uv_snapshot!(context.filters(), context.sync().arg("--package").arg("child").arg("--extra").arg("async"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 5 packages in [TIME]
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==4.3.0
+     + idna==3.6
+     + sniffio==1.3.1
+    "###);
+
+    Ok(())
+}
+
+#[test]
+fn sync_non_existent_extra_non_project_workspace() -> Result<()> {
+    let context = TestContext::new("3.12");
+
+    let pyproject_toml = context.temp_dir.child("pyproject.toml");
+    pyproject_toml.write_str(
+        r#"
+        [tool.uv.workspace]
+        members = ["child", "other"]
+        "#,
+    )?;
+
+    context
+        .temp_dir
+        .child("child")
+        .child("pyproject.toml")
+        .write_str(
+            r#"
+        [project]
+        name = "child"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+
+        [project.optional-dependencies]
+        async = ["anyio>3"]
+        "#,
+        )?;
+
+    context
+        .temp_dir
+        .child("other")
+        .child("pyproject.toml")
+        .write_str(
+            r#"
+        [project]
+        name = "other"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        "#,
+        )?;
+
+    context.lock().assert().success();
+
+    // Requesting an extra that only exists in the child should succeed, since we sync all members
+    // by default.
+    uv_snapshot!(context.filters(), context.sync().arg("--extra").arg("async"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 5 packages in [TIME]
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + anyio==4.3.0
+     + idna==3.6
+     + sniffio==1.3.1
+    "###);
+
+    // Syncing from the child should also succeed.
+    uv_snapshot!(context.filters(), context.sync().arg("--package").arg("child").arg("--extra").arg("async"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 5 packages in [TIME]
+    Audited 3 packages in [TIME]
+    "###);
+
+    // Syncing from an unrelated child should fail.
+    uv_snapshot!(context.filters(), context.sync().arg("--package").arg("other").arg("--extra").arg("async"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 5 packages in [TIME]
+    error: Extra `async` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    Ok(())
+}
+
 /// Regression test for <https://github.com/astral-sh/uv/issues/6316>.
 ///
 /// Previously, we would read metadata statically from pyproject.toml and write that to `uv.lock`. In