diff --git a/python/tests/test_runner.py b/python/tests/test_runner.py
index ae0783a..3f76baf 100644
--- a/python/tests/test_runner.py
+++ b/python/tests/test_runner.py
@@ -70,6 +70,30 @@ def test_exit_code_captured(self, tmp_path):
         )
         assert result.exit_code == 42
 
+    def test_timeout_returns_str_stdout_stderr(self, tmp_path):
+        """When the subprocess exceeds the timeout, partial output is
+        returned as decoded str (matching the success path) rather than
+        the raw bytes that subprocess.TimeoutExpired carries by default.
+        """
+        result = run_path(
+            [
+                sys.executable,
+                "-u",
+                "-c",
+                "import time; print('partial line'); time.sleep(5)",
+            ],
+            use_stdin=False,
+            cwd=str(tmp_path),
+            timeout=1,
+        )
+        # exit_code is None on timeout (process was killed)
+        assert result.exit_code is None
+        # stdout/stderr must be str, not bytes, regardless of whether
+        # the subprocess had produced any output before being killed
+        assert isinstance(result.stdout, str)
+        assert isinstance(result.stderr, str)
+        assert "partial line" in result.stdout
+
     def test_with_env(self, tmp_path):
         import os
 
diff --git a/python/vscode_common_python_lsp/runner.py b/python/vscode_common_python_lsp/runner.py
index f7939d0..ab8d939 100644
--- a/python/vscode_common_python_lsp/runner.py
+++ b/python/vscode_common_python_lsp/runner.py
@@ -133,7 +133,13 @@ def run_path(
                 timeout=timeout,
             )
         except subprocess.TimeoutExpired as e:
-            return RunResult(e.stdout or "", e.stderr or "", None)
+            # subprocess.run with encoding='utf-8' returns decoded str on the
+            # normal completion path, but TimeoutExpired still carries the
+            # raw bytes captured from the pipe before decoding — produce
+            # str here so RunResult is uniformly typed.
+            partial_out = e.stdout.decode("utf-8", errors="replace") if e.stdout else ""
+            partial_err = e.stderr.decode("utf-8", errors="replace") if e.stderr else ""
+            return RunResult(partial_out, partial_err, None)
         return RunResult(result.stdout, result.stderr, result.returncode)