diff --git a/project/paperbench/paperbench/judge/base.py b/project/paperbench/paperbench/judge/base.py
index e6bbc6e4..bf0c8fe4 100644
--- a/project/paperbench/paperbench/judge/base.py
+++ b/project/paperbench/paperbench/judge/base.py
@@ -163,7 +163,7 @@ async def grade(
             weight=task.weight,
             sub_tasks=graded_sub_tasks,
             score=weighted_score,
-            valid_score=True,
+            valid_score=all(child.valid_score for child in graded_sub_tasks),
             explanation="Aggregated score from sub-tasks.",
             judge_metadata=None,
         )
@@ -193,4 +193,4 @@ def get_logger(self, task: TaskNode) -> BoundLogger:
         run_logger.addHandler(log_file_handler)
         run_logger.propagate = False
 
-        return wrap_logger(run_logger)
+        return wrap_logger(run_logger)
\ No newline at end of file
diff --git a/project/paperbench/tests/unit/test_judge_validity.py b/project/paperbench/tests/unit/test_judge_validity.py
new file mode 100644
index 00000000..4dc0bf37
--- /dev/null
+++ b/project/paperbench/tests/unit/test_judge_validity.py
@@ -0,0 +1,95 @@
+from pathlib import Path
+
+import pytest
+
+from paperbench.judge.base import Judge
+from paperbench.judge.graded_task_node import GradedTaskNode
+from paperbench.rubric.tasks import TaskNode
+
+
+class ValidityJudge(Judge):
+    @property
+    def judge_type(self) -> str:
+        return "validity-test"
+
+    async def grade_leaf(self, task: TaskNode) -> GradedTaskNode:
+        raise NotImplementedError
+
+    async def grade_subtree(self, task: TaskNode) -> GradedTaskNode:
+        raise NotImplementedError
+
+
+def _leaf(node_id: str) -> TaskNode:
+    return TaskNode(
+        id=node_id,
+        requirements=node_id,
+        weight=1,
+        task_category="Code Development",
+    )
+
+
+@pytest.mark.asyncio
+async def test_aggregate_validity_propagates_child_grading_failure(tmp_path: Path) -> None:
+    good = _leaf("good")
+    bad = _leaf("bad")
+    root = TaskNode(
+        id="root",
+        requirements="root",
+        weight=1,
+        sub_tasks=[good, bad],
+    )
+    judge = ValidityJudge(
+        paper_path=tmp_path / "paper.pdf",
+        rubric=root,
+        addendum=None,
+        judge_addendum=None,
+        submission_dir=tmp_path,
+    )
+
+    async def grade_leaf(task: TaskNode) -> GradedTaskNode:
+        if task.id == "bad":
+            raise RuntimeError("judge failed")
+        return GradedTaskNode.from_task(
+            task,
+            score=1.0,
+            valid_score=True,
+            explanation="graded",
+        )
+
+    graded = await judge.grade(root, grade_leaf)
+
+    assert graded.score == 0.5
+    assert graded.valid_score is False
+    assert graded.sub_tasks[0].valid_score is True
+    assert graded.sub_tasks[1].valid_score is False
+
+
+@pytest.mark.asyncio
+async def test_aggregate_validity_remains_true_when_all_children_are_valid(tmp_path: Path) -> None:
+    children = [_leaf("a"), _leaf("b")]
+    root = TaskNode(
+        id="root",
+        requirements="root",
+        weight=1,
+        sub_tasks=children,
+    )
+    judge = ValidityJudge(
+        paper_path=tmp_path / "paper.pdf",
+        rubric=root,
+        addendum=None,
+        judge_addendum=None,
+        submission_dir=tmp_path,
+    )
+
+    async def grade_leaf(task: TaskNode) -> GradedTaskNode:
+        return GradedTaskNode.from_task(
+            task,
+            score=1.0,
+            valid_score=True,
+            explanation="graded",
+        )
+
+    graded = await judge.grade(root, grade_leaf)
+
+    assert graded.score == 1.0
+    assert graded.valid_score is True