diff --git a/src/tokenizer.py b/src/tokenizer.py
index 63ea7ca..e1819fa 100644
--- a/src/tokenizer.py
+++ b/src/tokenizer.py
@@ -508,6 +508,12 @@ def detokenize_to_period(token_ids: list[int]) -> ChordPeriod:
             pos_in_bar, positions_per_bar,
         )
 
+    if not bars:
+        raise ChordFormatError(
+            "token sequence produced no complete bars "
+            f"(last partial bar had {pos_in_bar}/{positions_per_bar} positions)"
+        )
+
     return ChordPeriod(
         title="detokenized",
         key=key,
diff --git a/tests/test_tokenizer.py b/tests/test_tokenizer.py
index 3abe24f..b457896 100644
--- a/tests/test_tokenizer.py
+++ b/tests/test_tokenizer.py
@@ -16,6 +16,7 @@ from src.tokenizer import (
     ID_TO_TOKEN,
     TOKEN_TO_ID,
     VOCAB,
+    ChordFormatError,
     ChordPeriod,
     detokenize_to_period,
     parse_chord_file,
@@ -206,3 +207,17 @@ class TestRoundTrip:
         t = parse_chord_symbol(recovered.bars[0][0])
         assert t.root == "A"
         assert t.quality == "m"
+
+    def test_empty_bar_sequence_raises(self):
+        # BOS + metadata only, then EOS — no body tokens → must raise
+        ids = [
+            TOKEN_TO_ID["<BOS>"],
+            TOKEN_TO_ID["MODE_major"],
+            TOKEN_TO_ID["TIME_4/4"],
+            TOKEN_TO_ID["SUB_4"],
+            TOKEN_TO_ID["STYLE_H1K0"],
+            TOKEN_TO_ID["FUNC_chorus"],
+            TOKEN_TO_ID["<EOS>"],
+        ]
+        with pytest.raises(ChordFormatError, match="no complete bars"):
+            detokenize_to_period(ids)