diff --git a/bot_bottle/sidecar_init.py b/bot_bottle/sidecar_init.py
index 8bfa984..2b303a6 100644
--- a/bot_bottle/sidecar_init.py
+++ b/bot_bottle/sidecar_init.py
@@ -245,7 +245,12 @@ class _Supervisor:
                             except ProcessLookupError:
                                 pass
 
-        return all(p.poll() is not None for _, p in self.procs)
+        done = all(p.poll() is not None for _, p in self.procs)
+        if done:
+            for _, p in self.procs:
+                if p.stdout is not None:
+                    p.stdout.close()
+        return done
 
     def exit_code(self) -> int:
         """Positive child failures win; otherwise report success.
@@ -335,6 +340,8 @@ class _Supervisor:
                     except ProcessLookupError:
                         pass
                     p.wait()
+            if p.stdout is not None:
+                p.stdout.close()
             self._logged_dead.discard(daemon_name)
             new_proc = _spawn(spec)
             self.procs[idx] = (spec, new_proc)
diff --git a/tests/unit/test_sidecar_init.py b/tests/unit/test_sidecar_init.py
index 88f0b9b..1256af0 100644
--- a/tests/unit/test_sidecar_init.py
+++ b/tests/unit/test_sidecar_init.py
@@ -14,6 +14,7 @@ import subprocess
 import sys
 import time
 import unittest
+import warnings
 from pathlib import Path
 from unittest.mock import patch
 
@@ -135,6 +136,10 @@ class TestSupervisor(unittest.TestCase):
     We don't go through `main()` because main installs signal
     handlers process-wide, which collides with the test runner."""
 
+    def setUp(self):
+        warnings.simplefilter("error", ResourceWarning)
+        self.addCleanup(warnings.resetwarnings)
+
     def _drive(self, sup: _Supervisor, max_wait_s: float = 6.0) -> int:
         deadline = time.monotonic() + max_wait_s
         while not sup.tick():