diff --git a/src/der.rs b/src/der.rs
index c4cad81b..bb8213c7 100644
--- a/src/der.rs
+++ b/src/der.rs
@@ -13,17 +13,72 @@
 // OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 
 use crate::{calendar, time, Error};
-pub use ring::io::{
-    der::{nested, Tag, CONSTRUCTED},
+pub(crate) use ring::io::{
+    der::{CONSTRUCTED, CONTEXT_SPECIFIC},
     Positive,
 };
 
+// Copied (and extended) from ring's src/der.rs
+#[allow(clippy::upper_case_acronyms)]
+#[derive(Clone, Copy, Eq, PartialEq)]
+#[repr(u8)]
+pub(crate) enum Tag {
+    Boolean = 0x01,
+    Integer = 0x02,
+    BitString = 0x03,
+    OctetString = 0x04,
+    OID = 0x06,
+    UTF8String = 0x0C,
+    Sequence = CONSTRUCTED | 0x10, // 0x30
+    Set = CONSTRUCTED | 0x11,      // 0x31
+    UTCTime = 0x17,
+    GeneralizedTime = 0x18,
+
+    #[allow(clippy::identity_op)]
+    ContextSpecificConstructed0 = CONTEXT_SPECIFIC | CONSTRUCTED | 0,
+    ContextSpecificConstructed1 = CONTEXT_SPECIFIC | CONSTRUCTED | 1,
+    ContextSpecificConstructed3 = CONTEXT_SPECIFIC | CONSTRUCTED | 3,
+}
+
+impl From<Tag> for usize {
+    #[allow(clippy::as_conversions)]
+    fn from(tag: Tag) -> Self {
+        tag as Self
+    }
+}
+
+impl From<Tag> for u8 {
+    #[allow(clippy::as_conversions)]
+    fn from(tag: Tag) -> Self {
+        tag as Self
+    } // XXX: narrowing conversion.
+}
+
 #[inline(always)]
-pub fn expect_tag_and_get_value<'a>(
+pub(crate) fn expect_tag_and_get_value<'a>(
     input: &mut untrusted::Reader<'a>,
     tag: Tag,
 ) -> Result<untrusted::Input<'a>, Error> {
-    ring::io::der::expect_tag_and_get_value(input, tag).map_err(|_| Error::BadDER)
+    let (actual_tag, inner) = read_tag_and_get_value(input)?;
+    if usize::from(tag) != usize::from(actual_tag) {
+        return Err(Error::BadDER);
+    }
+    Ok(inner)
+}
+
+// TODO: investigate taking decoder as a reference to reduce generated code
+// size.
+pub(crate) fn nested<'a, F, R, E: Copy>(
+    input: &mut untrusted::Reader<'a>,
+    tag: Tag,
+    error: E,
+    decoder: F,
+) -> Result<R, E>
+where
+    F: FnOnce(&mut untrusted::Reader<'a>) -> Result<R, E>,
+{
+    let inner = expect_tag_and_get_value(input, tag).map_err(|_| error)?;
+    inner.read_all(error, decoder)
 }
 
 pub struct Value<'a> {
@@ -36,7 +91,10 @@ impl<'a> Value<'a> {
     }
 }
 
-pub fn expect_tag<'a>(input: &mut untrusted::Reader<'a>, tag: Tag) -> Result<Value<'a>, Error> {
+pub(crate) fn expect_tag<'a>(
+    input: &mut untrusted::Reader<'a>,
+    tag: Tag,
+) -> Result<Value<'a>, Error> {
     let (actual_tag, value) = read_tag_and_get_value(input)?;
     if usize::from(tag) != usize::from(actual_tag) {
         return Err(Error::BadDER);
@@ -46,7 +104,7 @@ pub fn expect_tag<'a>(input: &mut untrusted::Reader<'a>, tag: Tag) -> Result<Val
 }
 
 #[inline(always)]
-pub fn read_tag_and_get_value<'a>(
+pub(crate) fn read_tag_and_get_value<'a>(
     input: &mut untrusted::Reader<'a>,
 ) -> Result<(u8, untrusted::Input<'a>), Error> {
     ring::io::der::read_tag_and_get_value(input).map_err(|_| Error::BadDER)
@@ -54,7 +112,7 @@ pub fn read_tag_and_get_value<'a>(
 
 // TODO: investigate taking decoder as a reference to reduce generated code
 // size.
-pub fn nested_of_mut<'a, E>(
+pub(crate) fn nested_of_mut<'a, E>(
     input: &mut untrusted::Reader<'a>,
     outer_tag: Tag,
     inner_tag: Tag,
@@ -75,7 +133,7 @@ where
     })
 }
 
-pub fn bit_string_with_no_unused_bits<'a>(
+pub(crate) fn bit_string_with_no_unused_bits<'a>(
     input: &mut untrusted::Reader<'a>,
 ) -> Result<untrusted::Input<'a>, Error> {
     nested(input, Tag::BitString, Error::BadDER, |value| {
@@ -89,7 +147,7 @@ pub fn bit_string_with_no_unused_bits<'a>(
 
 // Like mozilla::pkix, we accept the nonconformant explicit encoding of
 // the default value (false) for compatibility with real-world certificates.
-pub fn optional_boolean(input: &mut untrusted::Reader) -> Result<bool, Error> {
+pub(crate) fn optional_boolean(input: &mut untrusted::Reader) -> Result<bool, Error> {
     if !input.peek(Tag::Boolean.into()) {
         return Ok(false);
     }
@@ -102,15 +160,17 @@ pub fn optional_boolean(input: &mut untrusted::Reader) -> Result<bool, Error> {
     })
 }
 
-pub fn positive_integer<'a>(input: &'a mut untrusted::Reader) -> Result<Positive<'a>, Error> {
+pub(crate) fn positive_integer<'a>(
+    input: &'a mut untrusted::Reader,
+) -> Result<Positive<'a>, Error> {
     ring::io::der::positive_integer(input).map_err(|_| Error::BadDER)
 }
 
-pub fn small_nonnegative_integer(input: &mut untrusted::Reader) -> Result<u8, Error> {
+pub(crate) fn small_nonnegative_integer(input: &mut untrusted::Reader) -> Result<u8, Error> {
     ring::io::der::small_nonnegative_integer(input).map_err(|_| Error::BadDER)
 }
 
-pub fn time_choice(input: &mut untrusted::Reader) -> Result<time::Time, Error> {
+pub(crate) fn time_choice(input: &mut untrusted::Reader) -> Result<time::Time, Error> {
     let is_utc_time = input.peek(Tag::UTCTime.into());
     let expected_tag = if is_utc_time {
         Tag::UTCTime
diff --git a/src/name/verify.rs b/src/name/verify.rs
index 30e428ac..05659d75 100644
--- a/src/name/verify.rs
+++ b/src/name/verify.rs
@@ -63,10 +63,7 @@ pub fn check_name_constraints(
         if !inner.peek(subtrees_tag.into()) {
             return Ok(None);
         }
-        let subtrees = der::nested(inner, subtrees_tag, Error::BadDER, |tagged| {
-            der::expect_tag_and_get_value(tagged, der::Tag::Sequence)
-        })?;
-        Ok(Some(subtrees))
+        der::expect_tag_and_get_value(inner, subtrees_tag).map(Some)
     }
 
     let permitted_subtrees = parse_subtrees(input, der::Tag::ContextSpecificConstructed0)?;
@@ -160,6 +157,10 @@ fn check_presented_id_conforms_to_constraints_in_subtree(
                 dns_name::presented_id_matches_constraint(name, base).ok_or(Error::BadDER)
             }
 
+            (GeneralName::DirectoryName(name), GeneralName::DnsName(base)) => {
+                common_name(name).map(|cn| cn == base)
+            }
+
             (GeneralName::DirectoryName(name), GeneralName::DirectoryName(base)) => Ok(
                 presented_directory_name_matches_constraint(name, base, subtrees),
             ),
@@ -319,3 +320,18 @@ fn general_name<'a>(input: &mut untrusted::Reader<'a>) -> Result<GeneralName<'a>
     };
     Ok(name)
 }
+
+static COMMON_NAME: untrusted::Input = untrusted::Input::from(&[85, 4, 3]);
+
+fn common_name(input: untrusted::Input) -> Result<untrusted::Input, Error> {
+    let inner = &mut untrusted::Reader::new(input);
+    der::nested(inner, der::Tag::Set, Error::BadDER, |tagged| {
+        der::nested(tagged, der::Tag::Sequence, Error::BadDER, |tagged| {
+            let value = der::expect_tag_and_get_value(tagged, der::Tag::OID)?;
+            if value != COMMON_NAME {
+                return Err(Error::BadDER);
+            }
+            der::expect_tag_and_get_value(tagged, der::Tag::UTF8String)
+        })
+    })
+}
diff --git a/src/verify_cert.rs b/src/verify_cert.rs
index 722ba932..31734c5f 100644
--- a/src/verify_cert.rs
+++ b/src/verify_cert.rs
@@ -81,7 +81,7 @@ pub fn build_chain(
 
     loop_while_non_fatal_error(intermediate_certs, |cert_der| {
         let potential_issuer =
-            cert::parse_cert(untrusted::Input::from(*cert_der), EndEntityOrCa::Ca(cert))?;
+            cert::parse_cert(untrusted::Input::from(cert_der), EndEntityOrCa::Ca(cert))?;
 
         if potential_issuer.subject != cert.issuer {
             return Err(Error::UnknownIssuer);
diff --git a/tests/integration.rs b/tests/integration.rs
index 34270272..36788d57 100644
--- a/tests/integration.rs
+++ b/tests/integration.rs
@@ -53,6 +53,25 @@ pub fn netflix() {
     );
 }
 
+#[cfg(feature = "alloc")]
+#[test]
+pub fn wpt() {
+    let ee: &[u8] = include_bytes!("wpt/ee.der");
+    let ca = include_bytes!("wpt/ca.der");
+
+    let anchors = vec![webpki::TrustAnchor::try_from_cert_der(ca).unwrap()];
+    let anchors = webpki::TLSServerTrustAnchors(&anchors);
+
+    #[allow(clippy::unreadable_literal)] // TODO: Make this clear.
+    let time = webpki::Time::from_seconds_since_unix_epoch(1619256684);
+
+    let cert = webpki::EndEntityCert::try_from(ee).unwrap();
+    assert_eq!(
+        Ok(()),
+        cert.verify_is_valid_tls_server_cert(ALL_SIGALGS, &anchors, &[], time)
+    );
+}
+
 #[test]
 pub fn ed25519() {
     let ee: &[u8] = include_bytes!("ed25519/ee.der");
diff --git a/tests/wpt/ca.der b/tests/wpt/ca.der
new file mode 100644
index 00000000..f7d00160
Binary files /dev/null and b/tests/wpt/ca.der differ
diff --git a/tests/wpt/ee.der b/tests/wpt/ee.der
new file mode 100644
index 00000000..7160db5a
Binary files /dev/null and b/tests/wpt/ee.der differ