diff --git a/contrib/pyln-testing/pyln/testing/utils.py b/contrib/pyln-testing/pyln/testing/utils.py
index f0a4e2336bb6..a9c0f2d9e450 100644
--- a/contrib/pyln-testing/pyln/testing/utils.py
+++ b/contrib/pyln-testing/pyln/testing/utils.py
@@ -215,6 +215,12 @@ def __init__(self, outputDir, verbose=True):
         # pass it to the log matcher and not print it to stdout).
         self.log_filter = lambda line: False
 
+    def _cleanup_output_files(self):
+        self.stdout_write.close()
+        self.stderr_write.close()
+        self.stdout_read.close()
+        self.stderr_read.close()
+
     def start(self, stdin=None, stdout_redir=True, stderr_redir=True):
         """Start the underlying process and start monitoring it. If
         stdout_redir is false, you have to make sure logs go into
@@ -249,6 +255,7 @@ def stop(self, timeout=10):
             self.proc.kill()
 
         self.proc.wait()
+        self._cleanup_output_files()
         return self.proc.returncode
 
     def kill(self):