diff --git a/assayer/exporter.py b/assayer/exporter.py
index a3395ff..59ff353 100644
--- a/assayer/exporter.py
+++ b/assayer/exporter.py
@@ -4,6 +4,16 @@
 
 from assayer.models import ModelResult
 
+_FIELDNAMES = [
+    "model",
+    "output",
+    "tokens_input",
+    "tokens_output",
+    "latency_seconds",
+    "cost_usd",
+    "error",
+]
+
 
 def _to_dict(result: ModelResult) -> dict:
     return {
@@ -23,7 +33,7 @@ def export(results: list[ModelResult], path: str) -> None:
 
     if dest.suffix.lower() == ".csv":
         with dest.open("w", newline="", encoding="utf-8") as f:
-            writer = csv.DictWriter(f, fieldnames=list(records[0].keys()))
+            writer = csv.DictWriter(f, fieldnames=_FIELDNAMES)
             writer.writeheader()
             writer.writerows(records)
     else:
diff --git a/tests/test_exporter.py b/tests/test_exporter.py
index e82f48b..23dc1f3 100644
--- a/tests/test_exporter.py
+++ b/tests/test_exporter.py
@@ -6,7 +6,15 @@
 from assayer.exporter import export
 from assayer.models import ModelResult
 
-_EXPECTED_FIELDS = {"model", "output", "tokens_input", "tokens_output", "latency_seconds", "cost_usd", "error"}
+_EXPECTED_FIELDS = {
+    "model",
+    "output",
+    "tokens_input",
+    "tokens_output",
+    "latency_seconds",
+    "cost_usd",
+    "error",
+}
 
 
 def _results() -> list[ModelResult]:
@@ -93,6 +101,18 @@ def test_export_csv_has_all_headers(tmp_path):
         assert set(reader.fieldnames) == _EXPECTED_FIELDS
 
 
+def test_export_csv_empty_results_writes_headers(tmp_path):
+    path = tmp_path / "results.csv"
+    export([], str(path))
+
+    with path.open(encoding="utf-8") as f:
+        reader = csv.DictReader(f)
+        rows = list(reader)
+
+    assert set(reader.fieldnames or []) == _EXPECTED_FIELDS
+    assert rows == []
+
+
 def test_export_csv_case_insensitive_extension(tmp_path):
     path = tmp_path / "results.CSV"
     export(_results(), str(path))