diff --git a/tokenizers/src/models/bpe/serialization.rs b/tokenizers/src/models/bpe/serialization.rs
index 152586efb..98cc15102 100644
--- a/tokenizers/src/models/bpe/serialization.rs
+++ b/tokenizers/src/models/bpe/serialization.rs
@@ -30,14 +30,14 @@ impl Serialize for BPE {
             .map(|(pair, (rank, _))| (pair, rank))
             .collect();
         merges.sort_unstable_by_key(|k| *k.1);
-        let merges_str = merges
+        let merges = merges
             .into_iter()
-            .map(|(pair, _)| format!("{} {}", self.vocab_r[&pair.0], self.vocab_r[&pair.1]))
+            .map(|(pair, _)| (self.vocab_r[&pair.0].clone(), self.vocab_r[&pair.1].clone()))
             .collect::<Vec<_>>();
         let ordered_vocab = OrderedVocabIter::new(&self.vocab_r);
 
         model.serialize_field("vocab", &ordered_vocab)?;
-        model.serialize_field("merges", &merges_str)?;
+        model.serialize_field("merges", &merges)?;
 
         model.end()
     }
@@ -81,7 +81,14 @@ impl<'de> Visitor<'de> for BPEVisitor {
     {
         let mut builder = BpeBuilder::new();
         let mut vocab: Option<HashMap<String, u32>> = None;
-        let mut merges: Option<Vec<String>> = None;
+
+        #[derive(Debug, Deserialize)]
+        #[serde(untagged)]
+        enum MergeType {
+            Tuple(Vec<(String, String)>),
+            Legacy(Vec<String>),
+        }
+        let mut merges: Option<MergeType> = None;
         while let Some(key) = map.next_key::<String>()? {
             match key.as_ref() {
                 "dropout" => {
@@ -134,8 +141,12 @@ impl<'de> Visitor<'de> for BPEVisitor {
             }
         }
         if let (Some(vocab), Some(merges)) = (vocab, merges) {
-            let merges =
-                convert_merges_to_hashmap(merges.into_iter(), &vocab).map_err(Error::custom)?;
+            let merges = match merges {
+                MergeType::Tuple(merges) => merges,
+                MergeType::Legacy(merges) => {
+                    convert_merges_to_hashmap(merges.into_iter(), &vocab).map_err(Error::custom)?
+                }
+            };
             builder = builder.vocab_and_merges(vocab, merges);
             Ok(builder.build().map_err(Error::custom)?)
         } else {
@@ -167,13 +178,40 @@ mod test {
             .build()
             .unwrap();
 
+        let legacy = r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b":2,"ab":3},"merges":["a b"]}"#;
+        let legacy = serde_json::from_str(legacy).unwrap();
+        assert_eq!(bpe, legacy);
+
         let data = serde_json::to_string(&bpe).unwrap();
         assert_eq!(
             data,
-            r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b":2,"ab":3},"merges":["a b"]}"#
+            r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b":2,"ab":3},"merges":[["a","b"]]}"#
         );
         let reconstructed = serde_json::from_str(&data).unwrap();
+        assert_eq!(bpe, reconstructed);
 
+        // With a space in the token
+        let vocab: Vocab = [
+            ("<unk>".into(), 0),
+            ("a".into(), 1),
+            ("b c d".into(), 2),
+            ("ab c d".into(), 3),
+        ]
+        .iter()
+        .cloned()
+        .collect();
+        let bpe = BpeBuilder::default()
+            .vocab_and_merges(vocab, vec![("a".to_string(), "b c d".to_string())])
+            .unk_token("<unk>".to_string())
+            .ignore_merges(true)
+            .build()
+            .unwrap();
+        let data = serde_json::to_string(&bpe).unwrap();
+        assert_eq!(
+            data,
+            r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b c d":2,"ab c d":3},"merges":[["a","b c d"]]}"#
+        );
+        let reconstructed = serde_json::from_str(&data).unwrap();
         assert_eq!(bpe, reconstructed);
     }
 
diff --git a/tokenizers/src/models/mod.rs b/tokenizers/src/models/mod.rs
index e12e70ffc..cdfb731a8 100644
--- a/tokenizers/src/models/mod.rs
+++ b/tokenizers/src/models/mod.rs
@@ -312,11 +312,14 @@ mod tests {
             .unwrap();
 
         let model = ModelWrapper::BPE(bpe);
+        let legacy = r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b":2,"ab":3},"merges":["a b"]}"#;
+        let legacy = serde_json::from_str(legacy).unwrap();
+        assert_eq!(model, legacy);
 
         let data = serde_json::to_string(&model).unwrap();
         assert_eq!(
             data,
-            r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b":2,"ab":3},"merges":["a b"]}"#
+            r#"{"type":"BPE","dropout":null,"unk_token":"<unk>","continuing_subword_prefix":null,"end_of_word_suffix":null,"fuse_unk":false,"byte_fallback":false,"ignore_merges":true,"vocab":{"<unk>":0,"a":1,"b":2,"ab":3},"merges":[["a","b"]]}"#
         );
         let reconstructed = serde_json::from_str(&data).unwrap();
         assert_eq!(model, reconstructed);