diff --git a/tests/test_historical_predecessors.py b/tests/test_historical_predecessors.py
index bb97cb2..e1e6647 100644
--- a/tests/test_historical_predecessors.py
+++ b/tests/test_historical_predecessors.py
@@ -8,6 +8,8 @@ from pathlib import Path
 import sqlite3
 import tempfile
 import unittest
+from types import SimpleNamespace
+from unittest.mock import patch
 
 from paper_atlas.collectors.dblp import catalogue, XML_SHA
 from paper_atlas.collectors.dblp_records import collect, normalize_row
@@ -102,7 +104,9 @@ class HistoricalPredecessorTests(unittest.TestCase):
                 'snapshot_sha256': XML_SHA, 'candidate_sha256': hashlib.sha256(candidate.read_bytes()).hexdigest(),
                 'candidate_records': 1, 'candidate_family_counts': {'aips':1},
                 'record_types': {'proceedings':1,'inproceedings':1}}))
-            result = collect(db, root/'early', ['ICAPS'], candidates=candidate, through_year=1990)
+            # Tiny CI fixtures may live on tmpfs; production reserve is tested separately.
+            with patch('paper_atlas.collectors.dblp_records.shutil.disk_usage', return_value=SimpleNamespace(free=16*1024**3)):
+                result = collect(db, root/'early', ['ICAPS'], candidates=candidate, through_year=1990)
             self.assertEqual((result['normalized_records'],result['files'][0]['venue']), (1,'EPS'))
             for year, missing in [(1991,'ICAPS/ewsp'),(1997,'ICAPS/ecp')]:
                 out = root/str(year); out.mkdir(); sentinel=out/'previous.txt';sentinel.write_text('accepted previous output')