diff --git a/src/scp/scp_utils.py b/src/scp/scp_utils.py
index 824e980..b94a55b 100644
--- a/src/scp/scp_utils.py
+++ b/src/scp/scp_utils.py
@@ -27,6 +27,16 @@
 _pkg_dir = Path(__file__).resolve().parent
 
 
+def _new_quarantine_id(qdir: Path) -> str:
+    for _ in range(10):
+        qid = uuid.uuid4().hex
+        content_path = qdir / f"{qid}.txt"
+        meta_path = qdir / f"{qid}.json"
+        if not content_path.exists() and not meta_path.exists():
+            return qid
+    raise ValueError("unable to allocate unique quarantine_id")
+
+
 def _quarantine_dir() -> Path:
     env = os.environ.get("SCP_QUARANTINE_DIR")
     if env:
@@ -163,7 +173,7 @@ def quarantine(
     else:
         raise ValueError(f"unsupported quarantine layout: {layout!r}")
     qdir.mkdir(parents=True, exist_ok=True)
-    qid = str(uuid.uuid4())[:8]
+    qid = _new_quarantine_id(qdir)
     meta = {"quarantine_id": qid, "reason": reason, "source": source}
     meta_json = json.dumps(meta, indent=2)
     content_bytes = len(content.encode("utf-8", errors="replace"))
diff --git a/tests/test_security_regressions.py b/tests/test_security_regressions.py
index bbbc897..b61eb84 100644
--- a/tests/test_security_regressions.py
+++ b/tests/test_security_regressions.py
@@ -4,6 +4,7 @@
 
 import os
 import time
+import uuid
 
 import pytest
 
@@ -119,6 +120,26 @@ def test_quarantine_impossible_write_does_not_evict_existing_entries(tmp_path, m
     assert old_json.is_file()
 
 
+def test_quarantine_uses_full_uuid_to_avoid_prefix_collision(tmp_path, monkeypatch) -> None:
+    monkeypatch.setenv("SCP_QUARANTINE_DIR", str(tmp_path))
+    ids = iter(
+        [
+            uuid.UUID("aaaaaaaa-0000-0000-0000-000000000001"),
+            uuid.UUID("aaaaaaaa-0000-0000-0000-000000000002"),
+        ]
+    )
+    monkeypatch.setattr(scp_utils.uuid, "uuid4", lambda: next(ids))
+
+    first = scp_utils.quarantine("first quarantine evidence", reason="r1", source="s1")
+    second = scp_utils.quarantine("second quarantine evidence", reason="r2", source="s2")
+
+    assert first["quarantine_id"] != second["quarantine_id"]
+    first_path = tmp_path / f"{first['quarantine_id']}.txt"
+    second_path = tmp_path / f"{second['quarantine_id']}.txt"
+    assert first_path.read_text(encoding="utf-8") == "first quarantine evidence"
+    assert second_path.read_text(encoding="utf-8") == "second quarantine evidence"
+
+
 def test_registry_fetch_layout_counts_toward_total_quota(tmp_path, monkeypatch) -> None:
     """AppSec: registry_fetch/ writes must count toward SCP_QUARANTINE_MAX_TOTAL_BYTES."""
     from scp import quarantine_limits