diff --git a/src/attrs.rs b/src/attrs.rs
index d599508..becd77b 100644
--- a/src/attrs.rs
+++ b/src/attrs.rs
@@ -36,7 +36,7 @@ pub fn strip_trailing_attr(src: &str, defs: &HashMap<String, Attr>) -> (String,
     };
     let body = &trimmed[open + 1..trimmed.len() - 1];
     let body = body.strip_prefix(':').unwrap_or(body).trim();
-    if !looks_like_attrs(body) {
+    if !looks_like_attrs(body, defs) {
         return (src.trim().to_string(), Attr::default());
     }
     (
@@ -73,7 +73,7 @@ pub fn parse_braced_attr(src: &str, defs: &HashMap<String, Attr>) -> Option<(Att
         if ch == '}' {
             let body = &src[1..i];
             let body = body.strip_prefix(':').unwrap_or(body).trim();
-            if looks_like_attrs(body) {
+            if looks_like_attrs(body, defs) {
                 return Some((parse_attrs_body(body, defs), i + 1));
             }
             return None;
@@ -396,13 +396,13 @@ fn last_attr_open(s: &str) -> Option<usize> {
     last
 }
 
-fn looks_like_attrs(body: &str) -> bool {
+fn looks_like_attrs(body: &str, defs: &HashMap<String, Attr>) -> bool {
     let b = body.trim();
     b.starts_with('#')
         || b.starts_with('.')
         || b.contains('=')
         || b.split_whitespace()
-            .any(|t| t.starts_with('#') || t.starts_with('.') || t.contains('='))
+            .any(|t| t.starts_with('#') || t.starts_with('.') || t.contains('=') || defs.contains_key(t))
 }
 
 fn attr_tokens(body: &str) -> Vec<String> {
diff --git a/tests/test_focused.py b/tests/test_focused.py
index c0bca57..1963290 100644
--- a/tests/test_focused.py
+++ b/tests/test_focused.py
@@ -90,6 +90,20 @@ def test_balance_ignores_rawtext_and_voids():
     assert "</div>" not in html
     assert "<br />" in html
 
+def test_ald_reference_alone_in_block_ial():
+    expected = '<p id="id" class="cls">Some text</p>\n'
+    assert to_xhtml("{:note: #id .cls}\n\nSome text\n{: note}\n") == expected
+    assert to_xhtml("{:note: #id .cls}\n\nSome text\n{:note}\n") == expected
+    assert to_xhtml("{:note: #id .cls}\nSome text\n{: note}\n") == expected
+
+def test_ald_reference_alone_in_span_ial():
+    html = to_xhtml("{:note: .cls}\n\nA [word]{: note} here\n")
+    assert '<span class="cls">word</span>' in html
+
+def test_undefined_ald_reference_stays_literal():
+    assert to_xhtml("Some text\n{: nope}\n") == "<p>Some text\n{: nope}</p>\n"
+    assert "[word]{nope}" in to_xhtml("A [word]{nope} here\n")
+
 def test_long_nonascii_words_near_autolink_cap_do_not_error():
     for boundary in ("(", "a: ", "x '"):
         for count in (126, 127, 128, 129, 130, 200):