diff --git a/implementations/rust/preserves/src/value/text/reader.rs b/implementations/rust/preserves/src/value/text/reader.rs
index a9b3533..9feda60 100644
--- a/implementations/rust/preserves/src/value/text/reader.rs
+++ b/implementations/rust/preserves/src/value/text/reader.rs
@@ -313,6 +313,18 @@ impl<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'
         }
     }
 
+    fn read_set(&mut self, read_annotations: bool) -> io::Result<N> {
+        let items = self.upto(b'}', read_annotations)?;
+        let mut s = Set::<N>::new();
+        for i in items {
+            if s.contains(&i) {
+                return Err(io_syntax_error("Duplicate set element"));
+            }
+            s.insert(i);
+        }
+        Ok(N::new(s))
+    }
+
     fn read_dictionary(&mut self, read_annotations: bool) -> io::Result<N> {
         let mut d = Map::new();
         loop {
@@ -326,6 +338,9 @@ impl<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'
             if self.next_byte()? != b':' {
                 return Err(io_syntax_error("Missing expected key/value separator"));
             }
+            if d.contains_key(&k) {
+                return Err(io_syntax_error("Duplicate key"));
+            }
             let v = Reader::<N>::demand_next(self, read_annotations)?;
             d.insert(k, v);
         }
@@ -392,13 +407,12 @@ impl<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'
     for TextReader<'de, 'src, N, Dec, S>
 {
     fn next(&mut self, read_annotations: bool) -> io::Result<Option<N>> {
-        self.skip_whitespace();
-        let c = match self.peek() {
-            Ok(c) => c,
+        match self.peek() {
             Err(e) if is_eof_io_error(&e) => return Ok(None),
-            Err(e) => return Err(e.into()),
-        };
-        Ok(Some(match c {
+            _ => (),
+        }
+        self.skip_whitespace();
+        Ok(Some(match self.peek()? {
             b'"' => {
                 self.skip()?;
                 N::new(self.read_string(b'"')?)
@@ -429,9 +443,7 @@ impl<'de, 'src, N: NestedValue, Dec: DomainParse<N::Embedded>, S: BinarySource<'
                 match self.next_byte()? {
                     b'f' => N::new(false),
                     b't' => N::new(true),
-                    b'{' => N::new(Set::from_iter(
-                        self.upto(b'}', read_annotations)?.into_iter(),
-                    )),
+                    b'{' => self.read_set(read_annotations)?,
                     b'"' => self.read_literal_binary()?,
                     b'x' => match self.next_byte()? {
                         b'"' => N::new(&self.read_hex_binary()?[..]),