diff --git a/tests/test_token_ids_unique.py b/tests/test_token_ids_unique.py
new file mode 100644
index 0000000..08e534d
--- /dev/null
+++ b/tests/test_token_ids_unique.py
@@ -0,0 +1,40 @@
+# tests/test_token_ids_unique.py
+# Checks that token IDs are unique. We don't check token "names" (dict keys are unique by definition).
+
+import pytest
+import tiktoken
+from collections import defaultdict
+
+ENCODING_NAMES = tiktoken.list_encoding_names()
+
+@pytest.mark.parametrize("enc_name", ENCODING_NAMES)
+def test_special_token_ids_are_unique(enc_name):
+    """
+    Special tokens: no two different names should share the same token id.
+    """
+    enc = tiktoken.get_encoding(enc_name)
+    sp = getattr(enc, "_special_tokens", {})
+    if not sp:
+        pytest.skip(f"{enc_name}: no special tokens")
+
+    id2names = defaultdict(list)
+    for name, tid in sp.items():
+        id2names[tid].append(name)
+
+    dups = {tid: names for tid, names in id2names.items() if len(names) > 1}
+    assert not dups, f"{enc_name}: duplicated special token ids: {dups}"
+
+@pytest.mark.parametrize("enc_name", ENCODING_NAMES)
+def test_mergeable_token_ids_are_unique(enc_name):
+    """
+    Mergeable (vocab) tokens: token ids should be unique.
+    Note: some builds may not expose `_mergeable_ranks` on Python side; skip in that case.
+    """
+    enc = tiktoken.get_encoding(enc_name)
+    mr = getattr(enc, "_mergeable_ranks", None)
+    if not mr:
+        pytest.skip(f"{enc_name}: mergeable ranks not exposed")
+
+    ids = list(mr.values())
+    assert len(ids) == len(set(ids)), f"{enc_name}: duplicated mergeable token ids"
+
diff --git a/tiktoken_ext/openai_public.py b/tiktoken_ext/openai_public.py
index 02c9ee2..ce1c6bf 100644
--- a/tiktoken_ext/openai_public.py
+++ b/tiktoken_ext/openai_public.py
@@ -142,7 +142,12 @@ def o200k_harmony():
         "<|reserved_200010|>": 200010,
         "<|reserved_200011|>": 200011,
         "<|call|>": 200012,
-    } | {f"<|reserved_{i}|>": i for i in range(200013, 201088)}
+        "<|reserved_200013|>": 200013,
+        "<|reserved_200014|>": 200014,
+        "<|reserved_200015|>": 200015,
+        "<|reserved_200016|>": 200016,
+        "<|reserved_200017|>": 200017,
+    } | {f"<|reserved_{i}|>": i for i in range(200019, 201088)}
     return {
         "name": name,
         "pat_str": pat_str,