diff --git a/src/syntax.rs b/src/syntax.rs
index f8478fa..4cb6189 100644
--- a/src/syntax.rs
+++ b/src/syntax.rs
@@ -104,7 +104,7 @@ pub fn record_key(value: &str) -> Result<&str> {
 
 #[cfg(test)]
 mod tests {
-    use atrium_api::types::string::Handle;
+    use atrium_api::types::string::{AtIdentifier, Handle};
 
     use super::{SpaceRef, collection, did, record_key, space_ref, tid};
 
@@ -171,6 +171,26 @@ mod tests {
         }
     }
 
+    #[test]
+    fn atrium_at_identifier_validation_matches_official_syntax_fixtures() {
+        for value in fixture_cases(include_str!(
+            "../tests/fixtures/atproto-atidentifier-syntax-valid.txt"
+        )) {
+            assert!(
+                value.parse::<AtIdentifier>().is_ok(),
+                "rejected valid AT identifier `{value}`"
+            );
+        }
+        for value in fixture_cases(include_str!(
+            "../tests/fixtures/atproto-atidentifier-syntax-invalid.txt"
+        )) {
+            assert!(
+                value.parse::<AtIdentifier>().is_err(),
+                "accepted invalid AT identifier `{value}`"
+            );
+        }
+    }
+
     #[test]
     fn atrium_nsid_validation_matches_official_syntax_fixtures() {
         for value in fixture_cases(include_str!(
diff --git a/tests/fixtures/README.md b/tests/fixtures/README.md
index 7a65942..3fde301 100644
--- a/tests/fixtures/README.md
+++ b/tests/fixtures/README.md
@@ -43,6 +43,15 @@ Source:
 
 The fixtures are CC0-1.0 licensed.
 
+`atproto-atidentifier-syntax-{valid,invalid}.txt` are copied without
+modification from the matching files under `syntax/` in the same official
+fixture repository and commit.
+
+Source:
+<https://github.com/bluesky-social/atproto-interop-tests/tree/056e5741bb330757205d6b16db5266fffcae937b/syntax>
+
+The fixtures are CC0-1.0 licensed.
+
 `atproto-tid-syntax-{valid,invalid}.txt` are copied without modification from
 the matching files under `syntax/` in the official,
 implementation-neutral `bluesky-social/atproto-interop-tests` repository at
diff --git a/tests/fixtures/atproto-atidentifier-syntax-invalid.txt b/tests/fixtures/atproto-atidentifier-syntax-invalid.txt
new file mode 100644
index 0000000..f0f8430
--- /dev/null
+++ b/tests/fixtures/atproto-atidentifier-syntax-invalid.txt
@@ -0,0 +1,28 @@
+
+# invalid handles
+did:thing.test
+did:thing
+john-.test
+john.0
+john.-
+xn--bcher-.tld
+john..test
+jo_hn.test
+
+# invalid DIDs
+did
+didmethodval
+method:did:val
+did:method:
+didmethod:val
+did:methodval)
+:did:method:val
+did:method:val:
+did:method:val%
+DID:method:val
+
+# other invalid stuff
+email@example.com
+@handle@example.com
+@handle
+blah
diff --git a/tests/fixtures/atproto-atidentifier-syntax-valid.txt b/tests/fixtures/atproto-atidentifier-syntax-valid.txt
new file mode 100644
index 0000000..cc4a42b
--- /dev/null
+++ b/tests/fixtures/atproto-atidentifier-syntax-valid.txt
@@ -0,0 +1,15 @@
+
+# allows valid handles
+XX.LCS.MIT.EDU
+john.test
+jan.test
+a234567890123456789.test
+john2.test
+john-john.test
+
+# allows valid DIDs
+did:method:val
+did:method:VAL
+did:method:val123
+did:method:123
+did:method:val-two