diff --git a/tools/check_wave_corpus.py b/tools/check_wave_corpus.py
index 8428fd30..a66bf436 100755
--- a/tools/check_wave_corpus.py
+++ b/tools/check_wave_corpus.py
@@ -197,8 +197,11 @@ def main(argv: list[str] | None = None) -> int:
                     timeout=args.timeout,
                     check=False,
                 )
-            except subprocess.TimeoutExpired:
-                failures.append((relative, f"timed out after {args.timeout:g}s"))
+            except subprocess.TimeoutExpired as error:
+                detail = timeout_output(error)
+                failures.append(
+                    (relative, f"timed out after {args.timeout:g}s" + (f"\n{detail}" if detail else ""))
+                )
                 print(f"[TIMEOUT] {relative}")
                 continue
 
diff --git a/tools/test_check_wave_corpus.py b/tools/test_check_wave_corpus.py
index c2139bcf..06e7fb86 100644
--- a/tools/test_check_wave_corpus.py
+++ b/tools/test_check_wave_corpus.py
@@ -1,5 +1,6 @@
 import io
 import os
+import subprocess
 import tempfile
 import unittest
 from pathlib import Path
@@ -194,5 +195,29 @@ def test_no_override_and_no_binary_raises_file_not_found(self):
                     self.assertIn("wavec not found; build it or pass --wavec", str(cm.exception))
 
 
+class TestCorpusTimeout(unittest.TestCase):
+    def test_main_preserves_partial_timeout_output(self):
+        error = subprocess.TimeoutExpired(
+            ["wavec", "check"], 0.1, output="partial stdout", stderr="partial stderr"
+        )
+        with tempfile.TemporaryDirectory() as td:
+            root = Path(td)
+            source = root / "std" / "sample.wave"
+            source.parent.mkdir(parents=True)
+            source.write_text("fun main() -> i32 { return 0; }")
+            stdout = io.StringIO()
+            stderr = io.StringIO()
+            with patch.object(check_wave_corpus, "ROOT", root):
+                with patch.object(check_wave_corpus, "resolve_wavec", return_value=Path("wavec")):
+                    with patch.object(check_wave_corpus, "corpus_files", return_value=[source]):
+                        with patch.object(check_wave_corpus, "run_process", side_effect=error):
+                            with patch("sys.stdout", stdout), patch("sys.stderr", stderr):
+                                self.assertEqual(main(["--timeout=0.1"]), 1)
+
+        self.assertIn("timed out after 0.1s", stderr.getvalue())
+        self.assertIn("partial stdout", stderr.getvalue())
+        self.assertIn("partial stderr", stderr.getvalue())
+
+
 if __name__ == "__main__":
     unittest.main()