diff --git a/src/gluonnlp/embedding/token_embedding.py b/src/gluonnlp/embedding/token_embedding.py
index 171be71e9f..d22100e487 100644
--- a/src/gluonnlp/embedding/token_embedding.py
+++ b/src/gluonnlp/embedding/token_embedding.py
@@ -830,8 +830,6 @@ def serialize(self, file_path, compress=True):
 
         if not unknown_token:  # Store empty string instead of None
             unknown_token = ''
-        else:
-            assert unknown_token == idx_to_token[UNK_IDX]
 
         if not compress:
             np.savez(file=file_path, unknown_token=unknown_token,
diff --git a/tests/unittest/test_token_embedding.py b/tests/unittest/test_token_embedding.py
index 7f5a635332..eb82c65dcc 100644
--- a/tests/unittest/test_token_embedding.py
+++ b/tests/unittest/test_token_embedding.py
@@ -18,6 +18,7 @@
 # under the License.
 
 import functools
+import os
 
 import mxnet as mx
 import pytest
@@ -49,10 +50,11 @@ def __getitem__(self, tokens):
     [
         (None, None),
         (['<unk>', 'hello', 'world'], mx.nd.zeros(shape=[3, 300])),  # 300 == embsize
+        (['hello', 'world', '<unk>'], mx.nd.zeros(shape=[3, 300])),  # 300 == embsize
         (['hello', 'world'], mx.nd.zeros(shape=[2, 300])),  # 300 == embsize
     ])
 def test_token_embedding_constructor(unknown_token, init_unknown_vec, allow_extend, unknown_lookup,
-                                     idx_token_vec_mapping, embsize=300):
+                                     idx_token_vec_mapping, tmp_path, embsize=300):
     idx_to_token, idx_to_vec = idx_token_vec_mapping
 
     TokenEmbedding = functools.partial(
@@ -61,28 +63,40 @@ def test_token_embedding_constructor(unknown_token, init_unknown_vec, allow_exte
         unknown_lookup=unknown_lookup(embsize) if unknown_lookup is not None else None,
         idx_to_token=idx_to_token, idx_to_vec=idx_to_vec)
 
+    def test_serialization(emb, tmp_path=tmp_path):
+        emb_path = os.path.join(str(tmp_path), "emb.npz")
+        emb.serialize(emb_path)
+        loaded_emb = nlp.embedding.TokenEmbedding.deserialize(emb_path)
+        assert loaded_emb == emb
+
     ## Test "legacy" constructor
     if idx_to_token is None:
         emb = TokenEmbedding()
         assert len(emb.idx_to_token) == 1 if unknown_token else len(emb.idx_to_token) == 0
         # emb does not know the embsize, thus idx_to_vec could not be initialized
         assert emb.idx_to_vec is None
+        with pytest.raises(AttributeError):
+            # Cannot serialize as idx_to_vec is not initialized
+            test_serialization(emb)
 
         # Set unknown_token
         if unknown_token:
             emb[unknown_token] = mx.nd.zeros(embsize) - 1
             assert (emb[unknown_token].asnumpy() == mx.nd.zeros(embsize).asnumpy() - 1).all()
             assert emb.idx_to_vec.shape[1] == embsize
+            test_serialization(emb)
 
         if allow_extend:
             emb = TokenEmbedding()
             emb[unknown_token] = mx.nd.zeros(embsize) - 1
             assert emb.idx_to_vec.shape[1] == embsize
+            test_serialization(emb)
 
             emb = TokenEmbedding()
             emb['<some_token>'] = mx.nd.zeros(embsize) - 1
             assert emb.idx_to_vec.shape[0] == 2 if unknown_token else emb.idx_to_vec.shape[0] == 1
             assert (emb['<some_token>'].asnumpy() == (mx.nd.zeros(embsize) - 1).asnumpy()).all()
+            test_serialization(emb)
 
     ## Test with idx_to_vec and idx_to_token arguments
     else:
@@ -95,11 +109,13 @@ def test_token_embedding_constructor(unknown_token, init_unknown_vec, allow_exte
         else:
             assert emb.idx_to_token == idx_to_token
             assert (emb.idx_to_vec.asnumpy() == idx_to_vec.asnumpy()).all()
+        test_serialization(emb)
 
         if allow_extend:
             emb = TokenEmbedding()
             emb[unknown_token] = mx.nd.zeros(embsize) - 1
             assert emb.idx_to_vec.shape[1] == embsize
+            test_serialization(emb)
 
             emb = TokenEmbedding()
             emb['<some_token>'] = mx.nd.zeros(embsize) - 1
@@ -109,3 +125,4 @@ def test_token_embedding_constructor(unknown_token, init_unknown_vec, allow_exte
                 assert emb.idx_to_vec.shape[0] == len(idx_to_token) + 2
             else:
                 assert emb.idx_to_vec.shape[0] == len(idx_to_token) + 1
+            test_serialization(emb)