diff --git a/crates/uv-resolver/src/lock/mod.rs b/crates/uv-resolver/src/lock/mod.rs
index 2d2f27d01..63b59cf4e 100644
--- a/crates/uv-resolver/src/lock/mod.rs
+++ b/crates/uv-resolver/src/lock/mod.rs
@@ -2617,6 +2617,11 @@ impl Package {
     fn is_dynamic(&self) -> bool {
         self.id.version.is_none()
     }
+
+    /// Returns the extras the package provides, if any.
+    pub fn provides_extras(&self) -> Option<&Vec<ExtraName>> {
+        self.metadata.provides_extras.as_ref()
+    }
 }
 
 /// Attempts to construct a `VerbatimUrl` from the given normalized `Path`.
diff --git a/crates/uv/src/commands/project/install_target.rs b/crates/uv/src/commands/project/install_target.rs
index 066afe2cc..b9432e1ed 100644
--- a/crates/uv/src/commands/project/install_target.rs
+++ b/crates/uv/src/commands/project/install_target.rs
@@ -2,7 +2,9 @@ use std::borrow::Cow;
 use std::path::Path;
 use std::str::FromStr;
 
-use itertools::Either;
+use itertools::{Either, Itertools};
+
+use uv_configuration::ExtrasSpecification;
 use uv_distribution_types::Index;
 use uv_normalize::PackageName;
 use uv_pypi_types::{LenientRequirement, VerbatimParsedUrl};
@@ -11,6 +13,8 @@ use uv_scripts::Pep723Script;
 use uv_workspace::pyproject::{DependencyGroupSpecifier, Source, Sources, ToolUvSources};
 use uv_workspace::Workspace;
 
+use crate::commands::project::ProjectError;
+
 /// A target that can be installed from a lockfile.
 #[derive(Debug, Copy, Clone)]
 pub(crate) enum InstallTarget<'lock> {
@@ -230,4 +234,68 @@ impl<'lock> InstallTarget<'lock> {
             ),
         }
     }
+
+    /// Validate the extras requested by the [`ExtrasSpecification`].
+    #[allow(clippy::result_large_err)]
+    pub(crate) fn validate_extras(self, extras: &ExtrasSpecification) -> Result<(), ProjectError> {
+        let extras = match extras {
+            ExtrasSpecification::Some(extras) => {
+                if extras.is_empty() {
+                    return Ok(());
+                }
+                Either::Left(extras.iter())
+            }
+            ExtrasSpecification::Exclude(extras) => {
+                if extras.is_empty() {
+                    return Ok(());
+                }
+                Either::Right(extras.iter())
+            }
+            _ => return Ok(()),
+        };
+
+        match self {
+            Self::Project { lock, .. }
+            | Self::Workspace { lock, .. }
+            | Self::NonProjectWorkspace { lock, .. } => {
+                let member_packages: Vec<&Package> = lock
+                    .packages()
+                    .iter()
+                    .filter(|package| self.roots().contains(package.name()))
+                    .collect();
+
+                // If `provides-extra` is not set in any package, do not perform the check, as this
+                // means that the lock file was generated on a version of uv that predates when the
+                // feature was added.
+                if !member_packages
+                    .iter()
+                    .any(|package| package.provides_extras().is_some())
+                {
+                    return Ok(());
+                }
+
+                for extra in extras {
+                    if !member_packages.iter().any(|package| {
+                        package
+                            .provides_extras()
+                            .is_some_and(|provides_extras| provides_extras.contains(extra))
+                    }) {
+                        return match self {
+                            Self::Project { .. } => {
+                                Err(ProjectError::MissingExtraProject(extra.clone()))
+                            }
+                            _ => Err(ProjectError::MissingExtraWorkspace(extra.clone())),
+                        };
+                    }
+                }
+            }
+            Self::Script { .. } => {
+                // We shouldn't get here if the list is empty so we can assume it isn't
+                let extra = extras.into_iter().next().expect("non-empty extras").clone();
+                return Err(ProjectError::MissingExtraScript(extra));
+            }
+        }
+
+        Ok(())
+    }
 }
diff --git a/crates/uv/src/commands/project/mod.rs b/crates/uv/src/commands/project/mod.rs
index df62a2530..cd78e99a1 100644
--- a/crates/uv/src/commands/project/mod.rs
+++ b/crates/uv/src/commands/project/mod.rs
@@ -23,7 +23,7 @@ use uv_distribution_types::{
 use uv_fs::{LockedFile, Simplified, CWD};
 use uv_git::ResolvedRepositoryReference;
 use uv_installer::{SatisfiesResult, SitePackages};
-use uv_normalize::{GroupName, PackageName, DEV_DEPENDENCIES};
+use uv_normalize::{ExtraName, GroupName, PackageName, DEV_DEPENDENCIES};
 use uv_pep440::{Version, VersionSpecifiers};
 use uv_pep508::MarkerTreeContents;
 use uv_pypi_types::{ConflictPackage, ConflictSet, Conflicts, Requirement};
@@ -152,6 +152,15 @@ pub(crate) enum ProjectError {
     #[error("Default group `{0}` (from `tool.uv.default-groups`) is not defined in the project's `dependency-groups` table")]
     MissingDefaultGroup(GroupName),
 
+    #[error("Extra `{0}` is not defined in the project's `optional-dependencies` table")]
+    MissingExtraProject(ExtraName),
+
+    #[error("Extra `{0}` is not defined in any project's `optional-dependencies` table")]
+    MissingExtraWorkspace(ExtraName),
+
+    #[error("PEP 723 scripts do not support optional dependencies, but extra `{0}` was specified")]
+    MissingExtraScript(ExtraName),
+
     #[error("Supported environments must be disjoint, but the following markers overlap: `{0}` and `{1}`.\n\n{hint}{colon} replace `{1}` with `{2}`.", hint = "hint".bold().cyan(), colon = ":".bold())]
     OverlappingMarkers(String, String, String),
 
diff --git a/crates/uv/src/commands/project/sync.rs b/crates/uv/src/commands/project/sync.rs
index 5dc241b0c..a87a62ede 100644
--- a/crates/uv/src/commands/project/sync.rs
+++ b/crates/uv/src/commands/project/sync.rs
@@ -587,6 +587,7 @@ pub(super) async fn do_sync(
     }
 
     // Validate that the set of requested extras and development groups are compatible.
+    target.validate_extras(extras)?;
     detect_conflicts(target.lock(), extras, dev)?;
 
     // Determine the markers to use for resolution.
diff --git a/crates/uv/tests/it/lock_conflict.rs b/crates/uv/tests/it/lock_conflict.rs
index e79f8a0b8..5124e0119 100644
--- a/crates/uv/tests/it/lock_conflict.rs
+++ b/crates/uv/tests/it/lock_conflict.rs
@@ -4440,11 +4440,18 @@ conflicts = [
         "#,
     )?;
 
-    // I believe there are multiple valid solutions here, but the main
-    // thing is that `x2` should _not_ activate the `idna==3.4` dependency
-    // in `proxy1`. The `--extra=x2` should be a no-op, since there is no
-    // `x2` extra in the top level `pyproject.toml`.
+    // Error out, as x2 extra is only on the child.
     uv_snapshot!(context.filters(), context.sync().arg("--extra=x2"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 7 packages in [TIME]
+    error: Extra `x2` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    uv_snapshot!(context.filters(), context.sync(), @r###"
     success: true
     exit_code: 0
     ----- stdout -----
diff --git a/crates/uv/tests/it/sync.rs b/crates/uv/tests/it/sync.rs
index f42ff1ab2..56d165f15 100644
--- a/crates/uv/tests/it/sync.rs
+++ b/crates/uv/tests/it/sync.rs
@@ -2626,6 +2626,151 @@ fn sync_group_self() -> Result<()> {
     Ok(())
 }
 
+#[test]
+fn sync_non_existent_extra() -> 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"
+        [project.optional-dependencies]
+        types = ["sniffio>1"]
+        async = ["anyio>3"]
+        "#,
+    )?;
+
+    context.lock().assert().success();
+
+    // Requesting a non-existent extra should fail.
+    uv_snapshot!(context.filters(), context.sync().arg("--extra").arg("baz"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    error: Extra `baz` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    // Excluding a non-existing extra when requesting all extras should fail.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-extras").arg("--no-extra").arg("baz"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 4 packages in [TIME]
+    error: Extra `baz` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    Ok(())
+}
+
+#[test]
+fn sync_non_existent_extra_no_optional_dependencies() -> 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"
+        "#,
+    )?;
+
+    context.lock().assert().success();
+
+    // Requesting a non-existent extra should fail.
+    uv_snapshot!(context.filters(), context.sync().arg("--extra").arg("baz"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    error: Extra `baz` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    // Excluding a non-existing extra when requesting all extras should fail.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-extras").arg("--no-extra").arg("baz"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 1 package in [TIME]
+    error: Extra `baz` is not defined in the project's `optional-dependencies` table
+    "###);
+
+    Ok(())
+}
+
+/// Ensures that we do not perform validation of extras against a lock file that was generated on a
+/// version of uv that predates when `provides-extras` feature was added.
+#[test]
+fn sync_ignore_extras_check_when_no_provides_extras() -> 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"
+        [project.optional-dependencies]
+        types = ["sniffio>1"]
+        "#,
+    )?;
+
+    // Write a lockfile that does not have `provides-extra`, simulating a version that predates when
+    // the feature was added.
+    context.temp_dir.child("uv.lock").write_str(indoc! {r#"
+        version = 1
+        requires-python = ">=3.12"
+
+        [[package]]
+        name = "project"
+        version = "0.1.0"
+        source = { virtual = "." }
+
+        [package.optional-dependencies]
+        types = [
+            { name = "sniffio" },
+        ]
+
+        [package.metadata]
+        requires-dist = [{ name = "sniffio", marker = "extra == 'types'", specifier = ">1" }]
+
+        [[package]]
+        name = "sniffio"
+        version = "1.3.1"
+        source = { registry = "https://pypi.org/simple" }
+        sdist = { url = "https://files.pythonhosted.org/packages/a2/87/a6771e1546d97e7e041b6ae58d80074f81b7d5121207425c964ddf5cfdbd/sniffio-1.3.1.tar.gz", hash = "sha256:f4324edc670a0f49750a81b895f35c3adb843cca46f0530f79fc1babb23789dc", size = 20372 }
+        wheels = [
+            { url = "https://files.pythonhosted.org/packages/e9/44/75a9c9421471a6c4805dbf2356f7c181a29c1879239abab1ea2cc8f38b40/sniffio-1.3.1-py3-none-any.whl", hash = "sha256:2f6da418d1f1e0fddd844478f41680e794e6051915791a034ff65e5f100525a2", size = 10235 },
+        ]
+    "#})?;
+
+    // Requesting a non-existent extra should not fail, as no validation should be performed.
+    uv_snapshot!(context.filters(), context.sync().arg("--frozen").arg("--extra").arg("baz"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Audited in [TIME]
+    "###);
+
+    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
@@ -5397,7 +5542,7 @@ fn sync_all_extras() -> Result<()> {
      + typing-extensions==4.10.0
     "###);
 
-    // Sync all extras.
+    // Sync all extras excluding an extra that exists in both the parent and child.
     uv_snapshot!(context.filters(), context.sync().arg("--all-packages").arg("--all-extras").arg("--no-extra").arg("types"), @r###"
     success: true
     exit_code: 0
@@ -5409,6 +5554,139 @@ fn sync_all_extras() -> Result<()> {
      - typing-extensions==4.10.0
     "###);
 
+    // Sync an extra that doesn't exist.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-packages").arg("--extra").arg("foo"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 8 packages in [TIME]
+    error: Extra `foo` is not defined in any project's `optional-dependencies` table
+    "###);
+
+    // Sync all extras excluding an extra that doesn't exist.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-packages").arg("--all-extras").arg("--no-extra").arg("foo"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 8 packages in [TIME]
+    error: Extra `foo` is not defined in any project's `optional-dependencies` table
+    "###);
+
+    Ok(())
+}
+
+/// Sync all members in a workspace with dynamic extras.
+#[test]
+fn sync_all_extras_dynamic() -> 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"]
+        async = ["anyio>3"]
+
+        [build-system]
+        requires = ["setuptools>=42"]
+        build-backend = "setuptools.build_meta"
+
+        [tool.uv.workspace]
+        members = ["child"]
+
+        [tool.uv.sources]
+        child = { workspace = true }
+        "#,
+    )?;
+    context
+        .temp_dir
+        .child("src")
+        .child("project")
+        .child("__init__.py")
+        .touch()?;
+
+    // Add a workspace member.
+    let child = context.temp_dir.child("child");
+    child.child("pyproject.toml").write_str(
+        r#"
+        [project]
+        name = "child"
+        version = "0.1.0"
+        requires-python = ">=3.12"
+        dynamic = ["optional-dependencies"]
+
+        [tool.setuptools.dynamic.optional-dependencies]
+        dev = { file = "requirements-dev.txt" }
+
+        [build-system]
+        requires = ["setuptools>=42"]
+        build-backend = "setuptools.build_meta"
+        "#,
+    )?;
+    child
+        .child("src")
+        .child("child")
+        .child("__init__.py")
+        .touch()?;
+
+    child
+        .child("requirements-dev.txt")
+        .write_str("typing-extensions==4.10.0")?;
+
+    // Generate a lockfile.
+    context.lock().assert().success();
+
+    // Sync an extra that exists in the parent.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-packages").arg("--extra").arg("types"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 6 packages in [TIME]
+    Prepared 3 packages in [TIME]
+    Installed 3 packages in [TIME]
+     + child==0.1.0 (from file://[TEMP_DIR]/child)
+     + project==0.1.0 (from file://[TEMP_DIR]/)
+     + sniffio==1.3.1
+    "###);
+
+    // Sync a dynamic extra that exists in the child.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-packages").arg("--extra").arg("dev"), @r###"
+    success: true
+    exit_code: 0
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 6 packages in [TIME]
+    Prepared 1 package in [TIME]
+    Uninstalled 1 package in [TIME]
+    Installed 1 package in [TIME]
+     - sniffio==1.3.1
+     + typing-extensions==4.10.0
+    "###);
+
+    // Sync a dynamic extra that doesn't exist in the child.
+    uv_snapshot!(context.filters(), context.sync().arg("--all-packages").arg("--extra").arg("foo"), @r###"
+    success: false
+    exit_code: 2
+    ----- stdout -----
+
+    ----- stderr -----
+    Resolved 6 packages in [TIME]
+    error: Extra `foo` is not defined in any project's `optional-dependencies` table
+    "###);
+
     Ok(())
 }