diff --git a/gittensor/classes.py b/gittensor/classes.py
index 93bed5e1d..205a2b11f 100644
--- a/gittensor/classes.py
+++ b/gittensor/classes.py
@@ -708,6 +708,9 @@ def _build_cache_entry(evaluation: 'MinerEvaluation') -> 'MinerEvaluation':
         cached.merged_pull_requests = [_pr_for_cache(pr) for pr in evaluation.merged_pull_requests]
         cached.open_pull_requests = [_pr_for_cache(pr) for pr in evaluation.open_pull_requests]
         cached.closed_pull_requests = [_pr_for_cache(pr) for pr in evaluation.closed_pull_requests]
+        cached.mirror_merged_prs = [_scored_mirror_pr_for_cache(pr) for pr in evaluation.mirror_merged_prs]
+        cached.mirror_open_prs = [_scored_mirror_pr_for_cache(pr) for pr in evaluation.mirror_open_prs]
+        cached.mirror_closed_prs = [_scored_mirror_pr_for_cache(pr) for pr in evaluation.mirror_closed_prs]
         return cached
 
     @staticmethod
@@ -735,3 +738,9 @@ def _pr_with_fresh_issues(pr: 'PullRequest') -> 'PullRequest':
     if pr.issues is not None:
         pr_copy.issues = [copy.copy(issue) for issue in pr.issues]
     return pr_copy
+
+
+def _scored_mirror_pr_for_cache(scored: 'ScoredMirrorPR') -> 'ScoredMirrorPR':
+    scored_copy = copy.copy(scored)
+    scored_copy.files = None
+    return scored_copy
diff --git a/tests/validator/test_validator_cache_fallback.py b/tests/validator/test_validator_cache_fallback.py
index 89667d195..16e45ab08 100644
--- a/tests/validator/test_validator_cache_fallback.py
+++ b/tests/validator/test_validator_cache_fallback.py
@@ -4,6 +4,8 @@
 from typing import cast
 
 from gittensor.classes import FileChange, Issue, MinerEvaluation, MinerEvaluationCache, PRState, PullRequest
+from gittensor.utils.mirror.models import MirrorFile, MirrorPullRequest, MirrorReviewSummary
+from gittensor.validator.oss_contributions.mirror.scored_pr import ScoredMirrorPR
 from neurons.validator import Validator
 
 
@@ -175,3 +177,69 @@ def test_store_isolates_cache_from_source_issue_mutations(self):
         cached_issues = cached.merged_pull_requests[0].issues
         assert cached_issues is not None
         assert cached_issues[0].discovery_earned_score == 0.0
+
+
+def _make_mirror_pr_with_file_blob(blob: str, pr_number: int = 7) -> ScoredMirrorPR:
+    now = datetime.now(timezone.utc)
+    pr = MirrorPullRequest(
+        repo_full_name='owner/repo',
+        pr_number=pr_number,
+        title='cached mirror pr',
+        body=None,
+        state='MERGED',
+        author_github_id='12345',
+        author_login='miner',
+        author_association='CONTRIBUTOR',
+        created_at=now,
+        closed_at=None,
+        merged_at=now,
+        last_edited_at=None,
+        edited_after_merge=False,
+        hours_since_merge=0.0,
+        merged_by_login='maintainer',
+        base_ref='main',
+        head_ref='feature',
+        head_repo_full_name='owner/repo',
+        default_branch='main',
+        head_sha='abc',
+        base_sha='def',
+        merge_base_sha='def',
+        additions=1,
+        deletions=0,
+        commits_count=1,
+        scoring_data_stored=True,
+        review_summary=MirrorReviewSummary(),
+    )
+    scored = ScoredMirrorPR(pr=pr, base_score=8.0, token_score=12.0)
+    scored.files = [
+        MirrorFile(
+            filename='src/lib.py',
+            previous_filename=None,
+            status='modified',
+            additions=1,
+            deletions=0,
+            changes=1,
+            is_binary=False,
+            head_content=blob,
+            base_content=blob,
+        )
+    ]
+    return scored
+
+
+class TestMirrorCacheIsolation:
+    def test_cache_drops_mirror_files_without_mutating_source(self):
+        cache = MinerEvaluationCache()
+        source = MinerEvaluation(uid=1, hotkey='hotkey_1', github_id='12345', github_pat='secret')
+        source.mirror_merged_prs = [_make_mirror_pr_with_file_blob('A' * 10_000)]
+        cache.store(source)
+
+        assert source.github_pat == 'secret'
+        source_files = source.mirror_merged_prs[0].files
+        assert source_files is not None
+        assert source_files[0].head_content == 'A' * 10_000
+
+        cached = cache.get(uid=1, hotkey='hotkey_1', github_id='12345')
+        assert cached is not None
+        assert cached.github_pat is None
+        assert cached.mirror_merged_prs[0].files is None