diff --git a/git-ref/src/namespace.rs b/git-ref/src/namespace.rs
index 63f30204c45..f952107c421 100644
--- a/git-ref/src/namespace.rs
+++ b/git-ref/src/namespace.rs
@@ -1,6 +1,7 @@
 #![allow(missing_docs)]
 
 use crate::PartialName;
+use bstr::{BString, ByteSlice, ByteVec};
 use std::convert::TryInto;
 
 pub fn expand<'a, Name, E>(namespace: Name) -> Result<crate::mutable::FullName, expand::Error>
@@ -8,8 +9,19 @@ where
     Name: TryInto<PartialName<'a>, Error = E>,
     expand::Error: From<E>,
 {
-    let _namespace = namespace.try_into()?;
-    todo!("impl")
+    let namespace = namespace.try_into()?.0;
+    let mut out = BString::default();
+    for component in namespace.split_str(b"/") {
+        out.push_str("refs/namespaces/");
+        out.push_str(component);
+        out.push_str(b"/");
+    }
+    out.pop();
+    debug_assert!(
+        git_validate::reference::name(out.as_ref()).is_ok(),
+        "we always produce valid ref names"
+    );
+    Ok(crate::mutable::FullName(out))
 }
 
 pub mod expand {
diff --git a/git-ref/tests/namespace/mod.rs b/git-ref/tests/namespace/mod.rs
index ae8cfaf8967..54180d7309a 100644
--- a/git-ref/tests/namespace/mod.rs
+++ b/git-ref/tests/namespace/mod.rs
@@ -1,19 +1,31 @@
-mod expand {
+od expand {
     #[test]
     fn each_component_expands_to_the_namespace_prefix_individually() {
         assert_eq!(
             git_ref::namespace::expand("foo/bar").unwrap().as_bstr(),
-            "refs/namespaces/foo/refs/namespaces/bar/"
+            "refs/namespaces/foo/refs/namespaces/bar"
         )
     }
 
     #[test]
-    #[ignore]
-    fn only_backslashes_are_valid_component_separators() {}
+    fn backslashes_are_no_component_separators_and_invalid() {
+        assert!(matches!(
+            git_ref::namespace::expand("foo\\bar").expect_err("empty invalid"),
+            git_ref::namespace::expand::Error::RefnameValidation(git_validate::refname::Error::Tag(
+                git_validate::tag::name::Error::InvalidByte(byte)
+            ))if byte == "\\"
+        ));
+    }
 
     #[test]
-    #[ignore]
-    fn trailing_slashes_do_nothing() {}
+    fn trailing_slashes_are_not_allowed() {
+        assert!(matches!(
+            git_ref::namespace::expand("foo/").expect_err("empty invalid"),
+            git_ref::namespace::expand::Error::RefnameValidation(git_validate::refname::Error::Tag(
+                git_validate::tag::name::Error::EndsWithSlash
+            ))
+        ));
+    }
 
     #[test]
     fn empty_namespaces_are_not_allowed() {
@@ -24,4 +36,20 @@ mod expand {
             ))
         ));
     }
+    #[test]
+    fn bare_slashes_are_not_allowed() {
+        assert!(matches!(
+            git_ref::namespace::expand("/").expect_err("empty invalid"),
+            git_ref::namespace::expand::Error::RefnameValidation(git_validate::refname::Error::Tag(
+                git_validate::tag::name::Error::EndsWithSlash
+            ))
+        ));
+    }
+    #[test]
+    fn repeated_slashes_are_invalid() {
+        assert!(matches!(
+            git_ref::namespace::expand("foo//bar").expect_err("empty invalid"),
+            git_ref::namespace::expand::Error::RefnameValidation(git_validate::refname::Error::RepeatedSlash)
+        ));
+    }
 }
diff --git a/git-validate/src/tag.rs b/git-validate/src/tag.rs
index 9143c2d295e..46004ec8357 100644
--- a/git-validate/src/tag.rs
+++ b/git-validate/src/tag.rs
@@ -51,7 +51,7 @@ pub fn name(bytes: &BStr) -> Result<&BStr, name::Error> {
     for byte in bytes.iter() {
         match byte {
             b'\\' | b'^' | b':' | b'[' | b'?' | b' ' | b'~' | b'\0'..=b'\x1F' | b'\x7F' => {
-                return Err(name::Error::InvalidByte(bytes.into()))
+                return Err(name::Error::InvalidByte((&[*byte][..]).into()))
             }
             b'*' => return Err(name::Error::Asterisk),
             b'.' if previous == b'.' => return Err(name::Error::DoubleDot),