diff --git a/crates/typst-syntax/src/ast.rs b/crates/typst-syntax/src/ast.rs
index 2ea318a7f..65a91629f 100644
--- a/crates/typst-syntax/src/ast.rs
+++ b/crates/typst-syntax/src/ast.rs
@@ -848,9 +848,9 @@ impl MathAttach {
             .find_map(SyntaxNode::cast)
     }
 
-    /// Extract primes if present.
+    /// Extract attached primes if present.
     pub fn primes(&self) -> Option<MathPrimes> {
-        self.0.cast_first_match()
+        self.0.children().nth(1).and_then(|n| n.cast())
     }
 }
 
diff --git a/tests/ref/math/opticalsize.png b/tests/ref/math/opticalsize.png
index 905d3389f..bd67542bc 100644
Binary files a/tests/ref/math/opticalsize.png and b/tests/ref/math/opticalsize.png differ
diff --git a/tests/typ/math/opticalsize.typ b/tests/typ/math/opticalsize.typ
index 6edd24193..07027cbba 100644
--- a/tests/typ/math/opticalsize.typ
+++ b/tests/typ/math/opticalsize.typ
@@ -43,3 +43,7 @@ $a'_b^c$, $a_b'^c$, $a_b^c'$, $a_b'^c'^d'$
 $(a'_b')^(c'_d')$, $a'/b'$, $a_b'/c_d'$
 
 $∫'$, $∑'$, $ ∑'_S' $
+
+---
+// Test attaching primes only
+$a' = a^', a_', a_'''^''^'$
\ No newline at end of file