diff --git a/implementations/rust/oo/src/packed/reader.rs b/implementations/rust/oo/src/packed/reader.rs
index cbfbf01..f00aec6 100644
--- a/implementations/rust/oo/src/packed/reader.rs
+++ b/implementations/rust/oo/src/packed/reader.rs
@@ -249,29 +249,40 @@ impl<'de, S: BinarySource<'de>> PackedReader<'de, S> {
     }
 }
 
+impl From<Tag> for Option<NextToken> {
+    #[inline(always)]
+    fn from(tag: Tag) -> Self {
+        match tag {
+            Tag::False => Some(NextToken::Value(ValueClass::Atomic(AtomClass::Boolean))),
+            Tag::True => Some(NextToken::Value(ValueClass::Atomic(AtomClass::Boolean))),
+            Tag::Float => Some(NextToken::Value(ValueClass::Atomic(AtomClass::Float))),
+            Tag::Double => Some(NextToken::Value(ValueClass::Atomic(AtomClass::Double))),
+            Tag::Annotation => Some(NextToken::Annotation),
+            Tag::Embedded => Some(NextToken::Value(ValueClass::Embedded)),
+            Tag::SmallInteger(_) => Some(NextToken::Value(ValueClass::Atomic(AtomClass::SignedInteger))),
+            Tag::MediumInteger(_) => Some(NextToken::Value(ValueClass::Atomic(AtomClass::SignedInteger))),
+            Tag::SignedInteger => Some(NextToken::Value(ValueClass::Atomic(AtomClass::SignedInteger))),
+            Tag::String => Some(NextToken::Value(ValueClass::Atomic(AtomClass::String))),
+            Tag::ByteString => Some(NextToken::Value(ValueClass::Atomic(AtomClass::ByteString))),
+            Tag::Symbol => Some(NextToken::Value(ValueClass::Atomic(AtomClass::Symbol))),
+            Tag::Record => Some(NextToken::Value(ValueClass::Compound(CompoundClass::Record))),
+            Tag::Sequence => Some(NextToken::Value(ValueClass::Compound(CompoundClass::Sequence))),
+            Tag::Set => Some(NextToken::Value(ValueClass::Compound(CompoundClass::Set))),
+            Tag::Dictionary => Some(NextToken::Value(ValueClass::Compound(CompoundClass::Dictionary))),
+            Tag::End => None,
+        }
+    }
+}
+
 impl<'de, S: BinarySource<'de>> Reader<'de> for PackedReader<'de, S> {
     fn peek_class(&mut self) -> io::Result<Option<NextToken>> {
-        match Tag::try_from(match self.peek()? {
+        let tag = Tag::try_from(match self.peek()? {
             None => return Ok(None),
             Some(b) => b,
-        })? {
-            Tag::False => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::Boolean)))),
-            Tag::True => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::Boolean)))),
-            Tag::Float => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::Float)))),
-            Tag::Double => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::Double)))),
-            Tag::Annotation => Ok(Some(NextToken::Annotation)),
-            Tag::Embedded => Ok(Some(NextToken::Value(ValueClass::Embedded))),
-            Tag::SmallInteger(_) => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::SignedInteger)))),
-            Tag::MediumInteger(_) => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::SignedInteger)))),
-            Tag::SignedInteger => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::SignedInteger)))),
-            Tag::String => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::String)))),
-            Tag::ByteString => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::ByteString)))),
-            Tag::Symbol => Ok(Some(NextToken::Value(ValueClass::Atomic(AtomClass::Symbol)))),
-            Tag::Record => Ok(Some(NextToken::Value(ValueClass::Compound(CompoundClass::Record)))),
-            Tag::Sequence => Ok(Some(NextToken::Value(ValueClass::Compound(CompoundClass::Sequence)))),
-            Tag::Set => Ok(Some(NextToken::Value(ValueClass::Compound(CompoundClass::Set)))),
-            Tag::Dictionary => Ok(Some(NextToken::Value(ValueClass::Compound(CompoundClass::Dictionary)))),
-            tag @ Tag::End => Err(self.syntax_error(&format!("Invalid tag: {:?}", tag))),
+        })?;
+        match tag.into() {
+            Some(n) => Ok(Some(n)),
+            None => Err(self.syntax_error("Unexpected tag")),
         }
     }