diff --git a/scripts/engine-bench-report.py b/scripts/engine-bench-report.py
index a38579c..698f54d 100755
--- a/scripts/engine-bench-report.py
+++ b/scripts/engine-bench-report.py
@@ -6,16 +6,16 @@
     engine-bench-report.py <results_dir> [--baseline <dir>] [--markdown <path>]
 
 Reads `combined_latency.csv` from `results_dir`, aggregates per-block data into
-headline throughput and latency metrics, uses `summary.csv` existence only as
-a benchmark-completion marker, resolves a report status
+headline throughput and latency metrics, uses a non-empty `summary.csv` as a
+benchmark-completion marker, resolves a report status
 (`normal`/`partial`/`no_data`/`error`), and prints a JSON analysis document to
 stdout. Callers (e.g., CI) parse the JSON directly.
 
 With `--baseline <dir>`, averages the headline metrics across prior-run
 complete prior runs under `<dir>/<run_id>/{summary,combined_latency}.csv`,
-where `summary.csv` is only a completion marker, and emits a Δ table alongside
-current values, flagging regressions against the trailing average. Incomplete
-baseline runs are skipped.
+where a non-empty `summary.csv` is the completion marker, and emits a Δ table
+alongside current values, flagging regressions against the trailing average.
+Incomplete baseline runs are skipped.
 
 With `--markdown <path>`, also renders a markdown report at that path.
 
@@ -180,8 +180,12 @@ def _load_combined_rows(path):
 
 def summary_marker_status(results_dir):
     path = os.path.join(results_dir, "summary.csv")
-    if not os.path.exists(path):
+    try:
+        size = os.path.getsize(path)
+    except FileNotFoundError:
         return SUMMARY_MARKER_MISSING
+    if size == 0:
+        return SUMMARY_MARKER_EMPTY
     return SUMMARY_MARKER_PRESENT
 
 
diff --git a/scripts/test_engine_bench_report.py b/scripts/test_engine_bench_report.py
new file mode 100644
index 0000000..d648ceb
--- /dev/null
+++ b/scripts/test_engine_bench_report.py
@@ -0,0 +1,55 @@
+#!/usr/bin/env python3
+"""Unit tests for engine-bench-report.py."""
+
+import importlib.util
+import tempfile
+import unittest
+from pathlib import Path
+
+
+SCRIPT_PATH = Path(__file__).with_name("engine-bench-report.py")
+SPEC = importlib.util.spec_from_file_location("engine_bench_report", SCRIPT_PATH)
+REPORT = importlib.util.module_from_spec(SPEC)
+SPEC.loader.exec_module(REPORT)
+
+
+class TestSummaryMarkerStatus(unittest.TestCase):
+    def test_missing_summary_is_incomplete(self):
+        with tempfile.TemporaryDirectory() as results_dir:
+            self.assertEqual(
+                REPORT.summary_marker_status(results_dir),
+                REPORT.SUMMARY_MARKER_MISSING,
+            )
+
+    def test_empty_summary_is_incomplete(self):
+        with tempfile.TemporaryDirectory() as results_dir:
+            Path(results_dir, "summary.csv").touch()
+
+            self.assertEqual(
+                REPORT.summary_marker_status(results_dir),
+                REPORT.SUMMARY_MARKER_EMPTY,
+            )
+
+    def test_non_empty_summary_is_complete(self):
+        with tempfile.TemporaryDirectory() as results_dir:
+            Path(results_dir, "summary.csv").write_text(
+                "block_number,new_payload_ms\n",
+                encoding="utf-8",
+            )
+
+            self.assertEqual(
+                REPORT.summary_marker_status(results_dir),
+                REPORT.SUMMARY_MARKER_PRESENT,
+            )
+
+    def test_empty_summary_makes_report_partial(self):
+        status = REPORT.resolve_report_status(
+            REPORT.SUMMARY_MARKER_EMPTY,
+            {"samples": 1},
+        )
+
+        self.assertEqual(status, REPORT.REPORT_STATUS_PARTIAL)
+
+
+if __name__ == "__main__":
+    unittest.main()