diff --git a/crates/cargo-util-schemas/src/restricted_names.rs b/crates/cargo-util-schemas/src/restricted_names.rs
index 36df8ce46..40f22197a 100644
--- a/crates/cargo-util-schemas/src/restricted_names.rs
+++ b/crates/cargo-util-schemas/src/restricted_names.rs
@@ -34,7 +34,10 @@ enum ErrorKind {
 }
 
 pub(crate) fn validate_package_name(name: &str) -> Result<()> {
-    validate_name(name, "package name")
+    for part in name.split("::") {
+        validate_name(part, "package name")?;
+    }
+    Ok(())
 }
 
 pub(crate) fn validate_registry_name(name: &str) -> Result<()> {
@@ -86,6 +89,17 @@ pub(crate) fn validate_name(name: &str, what: &'static str) -> Result<()> {
 
 /// Ensure a package name is [valid][validate_package_name]
 pub(crate) fn sanitize_package_name(name: &str, placeholder: char) -> String {
+    let mut slug = String::new();
+    for part in name.split("::") {
+        if !slug.is_empty() {
+            slug.push_str("::");
+        }
+        slug.push_str(&sanitize_name(part, placeholder));
+    }
+    slug
+}
+
+pub(crate) fn sanitize_name(name: &str, placeholder: char) -> String {
     let mut slug = String::new();
     let mut chars = name.chars();
     while let Some(ch) = chars.next() {
diff --git a/src/cargo/util/toml/mod.rs b/src/cargo/util/toml/mod.rs
index 7470c333d..bdab8260c 100644
--- a/src/cargo/util/toml/mod.rs
+++ b/src/cargo/util/toml/mod.rs
@@ -247,6 +247,16 @@ pub fn prepare_for_publish(
     package_root: &Path,
 ) -> CargoResult<manifest::TomlManifest> {
     let gctx = ws.gctx();
+
+    if me
+        .cargo_features
+        .iter()
+        .flat_map(|f| f.iter())
+        .any(|f| f == "open-namespaces")
+    {
+        anyhow::bail!("cannot publish with `open-namespaces`")
+    }
+
     let mut package = me.package().unwrap().clone();
     package.workspace = None;
     let current_resolver = package
@@ -587,6 +597,9 @@ pub fn to_real_manifest(
     };
 
     let package_name = package.name.trim();
+    if package_name.contains(':') {
+        features.require(Feature::open_namespaces())?;
+    }
 
     let resolved_path = package_root.join("Cargo.toml");
 
diff --git a/tests/testsuite/build.rs b/tests/testsuite/build.rs
index c7c751b50..23944d93e 100644
--- a/tests/testsuite/build.rs
+++ b/tests/testsuite/build.rs
@@ -467,18 +467,18 @@ fn cargo_compile_with_empty_package_name() {
 #[cargo_test]
 fn cargo_compile_with_invalid_package_name() {
     let p = project()
-        .file("Cargo.toml", &basic_manifest("foo::bar", "0.0.0"))
+        .file("Cargo.toml", &basic_manifest("foo@bar", "0.0.0"))
         .build();
 
     p.cargo("build")
         .with_status(101)
         .with_stderr(
             "\
-[ERROR] invalid character `:` in package name: `foo::bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
+[ERROR] invalid character `@` in package name: `foo@bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
  --> Cargo.toml:3:16
   |
-3 |         name = \"foo::bar\"
-  |                ^^^^^^^^^^
+3 |         name = \"foo@bar\"
+  |                ^^^^^^^^^
   |
 ",
         )
diff --git a/tests/testsuite/open_namespaces.rs b/tests/testsuite/open_namespaces.rs
index e55818432..1a1972602 100644
--- a/tests/testsuite/open_namespaces.rs
+++ b/tests/testsuite/open_namespaces.rs
@@ -20,14 +20,15 @@ fn within_namespace_requires_feature() {
         .masquerade_as_nightly_cargo(&["open-namespaces"])
         .with_status(101)
         .with_stderr(
-            "\
-[ERROR] invalid character `:` in package name: `foo::bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
- --> Cargo.toml:3:24
-  |
-3 |                 name = \"foo::bar\"
-  |                        ^^^^^^^^^^
-  |
-",
+            r#"error: failed to parse manifest at `[CWD]/Cargo.toml`
+
+Caused by:
+  feature `open-namespaces` is required
+
+  The package requires the Cargo feature called `open-namespaces`, but that feature is not stabilized in this version of Cargo ([..]).
+  Consider adding `cargo-features = ["open-namespaces"]` to the top of Cargo.toml (above the [package] table) to tell Cargo you are opting in to use this unstable feature.
+  See https://doc.rust-lang.org/nightly/cargo/reference/unstable.html#open-namespaces for more information about the status of this feature.
+"#,
         )
         .run()
 }
@@ -51,17 +52,50 @@ fn implicit_lib_within_namespace() {
 
     p.cargo("read-manifest")
         .masquerade_as_nightly_cargo(&["open-namespaces"])
-        .with_status(101)
-        .with_stderr(
-            "\
-[ERROR] invalid character `:` in package name: `foo::bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
- --> Cargo.toml:5:24
-  |
-5 |                 name = \"foo::bar\"
-  |                        ^^^^^^^^^^
-  |
-",
+        .with_json(
+            r#"{
+  "authors": [],
+  "categories": [],
+  "default_run": null,
+  "dependencies": [],
+  "description": null,
+  "documentation": null,
+  "edition": "2015",
+  "features": {},
+  "homepage": null,
+  "id": "path+file://[..]#foo::bar@0.0.1",
+  "keywords": [],
+  "license": null,
+  "license_file": null,
+  "links": null,
+  "manifest_path": "[CWD]/Cargo.toml",
+  "metadata": null,
+  "name": "foo::bar",
+  "publish": null,
+  "readme": null,
+  "repository": null,
+  "rust_version": null,
+  "source": null,
+  "targets": [
+    {
+      "crate_types": [
+        "lib"
+      ],
+      "doc": true,
+      "doctest": true,
+      "edition": "2015",
+      "kind": [
+        "lib"
+      ],
+      "name": "foo::bar",
+      "src_path": "[CWD]/src/lib.rs",
+      "test": true
+    }
+  ],
+  "version": "0.0.1"
+}"#,
         )
+        .with_stderr("")
         .run()
 }
 
@@ -84,17 +118,50 @@ fn implicit_bin_within_namespace() {
 
     p.cargo("read-manifest")
         .masquerade_as_nightly_cargo(&["open-namespaces"])
-        .with_status(101)
-        .with_stderr(
-            "\
-[ERROR] invalid character `:` in package name: `foo::bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
- --> Cargo.toml:5:24
-  |
-5 |                 name = \"foo::bar\"
-  |                        ^^^^^^^^^^
-  |
-",
+        .with_json(
+            r#"{
+  "authors": [],
+  "categories": [],
+  "default_run": null,
+  "dependencies": [],
+  "description": null,
+  "documentation": null,
+  "edition": "2015",
+  "features": {},
+  "homepage": null,
+  "id": "path+file://[..]#foo::bar@0.0.1",
+  "keywords": [],
+  "license": null,
+  "license_file": null,
+  "links": null,
+  "manifest_path": "[CWD]/Cargo.toml",
+  "metadata": null,
+  "name": "foo::bar",
+  "publish": null,
+  "readme": null,
+  "repository": null,
+  "rust_version": null,
+  "source": null,
+  "targets": [
+    {
+      "crate_types": [
+        "bin"
+      ],
+      "doc": true,
+      "doctest": false,
+      "edition": "2015",
+      "kind": [
+        "bin"
+      ],
+      "name": "foo::bar",
+      "src_path": "[CWD]/src/main.rs",
+      "test": true
+    }
+  ],
+  "version": "0.0.1"
+}"#,
         )
+        .with_stderr("")
         .run()
 }
 
@@ -116,22 +183,69 @@ fn explicit_bin_within_namespace() {
             "#,
         )
         .file("src/lib.rs", "")
-        .file("src/foo-bar/main.rs", "fn main() {}")
+        .file("src/bin/foo-bar/main.rs", "fn main() {}")
         .build();
 
     p.cargo("read-manifest")
         .masquerade_as_nightly_cargo(&["open-namespaces"])
-        .with_status(101)
-        .with_stderr(
-            "\
-[ERROR] invalid character `:` in package name: `foo::bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
- --> Cargo.toml:5:24
-  |
-5 |                 name = \"foo::bar\"
-  |                        ^^^^^^^^^^
-  |
-",
+        .with_json(
+            r#"{
+  "authors": [],
+  "categories": [],
+  "default_run": null,
+  "dependencies": [],
+  "description": null,
+  "documentation": null,
+  "edition": "2015",
+  "features": {},
+  "homepage": null,
+  "id": "path+file://[..]#foo::bar@0.0.1",
+  "keywords": [],
+  "license": null,
+  "license_file": null,
+  "links": null,
+  "manifest_path": "[CWD]/Cargo.toml",
+  "metadata": null,
+  "name": "foo::bar",
+  "publish": null,
+  "readme": null,
+  "repository": null,
+  "rust_version": null,
+  "source": null,
+  "targets": [
+    {
+      "crate_types": [
+        "lib"
+      ],
+      "doc": true,
+      "doctest": true,
+      "edition": "2015",
+      "kind": [
+        "lib"
+      ],
+      "name": "foo::bar",
+      "src_path": "[CWD]/src/lib.rs",
+      "test": true
+    },
+    {
+      "crate_types": [
+        "bin"
+      ],
+      "doc": true,
+      "doctest": false,
+      "edition": "2015",
+      "kind": [
+        "bin"
+      ],
+      "name": "foo-bar",
+      "src_path": "[CWD]/src/bin/foo-bar/main.rs",
+      "test": true
+    }
+  ],
+  "version": "0.0.1"
+}"#,
         )
+        .with_stderr("")
         .run()
 }
 
@@ -164,14 +278,14 @@ fn main() {}
   "edition": "2021",
   "features": {},
   "homepage": null,
-  "id": "path+file://[..]#foo--bar@0.0.0",
+  "id": "path+file://[..]#foo::bar@0.0.0",
   "keywords": [],
   "license": null,
   "license_file": null,
   "links": null,
   "manifest_path": "[CWD]/foo::bar.rs",
   "metadata": null,
-  "name": "foo--bar",
+  "name": "foo::bar",
   "publish": [],
   "readme": null,
   "repository": null,
@@ -188,7 +302,7 @@ fn main() {}
       "kind": [
         "bin"
       ],
-      "name": "foo--bar",
+      "name": "foo::bar",
       "src_path": "[..]/foo::bar.rs",
       "test": true
     }
@@ -197,14 +311,12 @@ fn main() {}
 }
 "#,
         )
-        .with_stderr(
-            "\
-",
-        )
+        .with_stderr("")
         .run();
 }
 
 #[cargo_test]
+#[cfg(unix)] // until we get proper packaging support
 fn publish_namespaced() {
     let registry = RegistryBuilder::new().http_api().http_index().build();
 
@@ -232,12 +344,14 @@ fn publish_namespaced() {
         .with_status(101)
         .with_stderr(
             "\
-[ERROR] invalid character `:` in package name: `foo::bar`, characters must be Unicode XID characters (numbers, `-`, `_`, or most letters)
- --> Cargo.toml:5:24
-  |
-5 |                 name = \"foo::bar\"
-  |                        ^^^^^^^^^^
-  |
+[UPDATING] crates.io index
+[WARNING] manifest has no documentation, homepage or repository.
+See https://doc.rust-lang.org/cargo/reference/manifest.html#package-metadata for more info.
+   Packaging foo::bar v0.0.1 ([CWD])
+[ERROR] failed to prepare local package for uploading
+
+Caused by:
+  cannot publish with `open-namespaces`
 ",
         )
         .run();