diff --git a/.gitlab-ci/bare-metal/cros_servo_run.py b/.gitlab-ci/bare-metal/cros_servo_run.py
index 995e1121066..23cebb0abee 100755
--- a/.gitlab-ci/bare-metal/cros_servo_run.py
+++ b/.gitlab-ci/bare-metal/cros_servo_run.py
@@ -50,12 +50,18 @@ class CrosServoRun:
             target=self.iter_feed_queue, daemon=True, args=(self.cpu_ser.lines(),))
         self.iter_feed_cpu.start()
 
+    def close(self):
+        self.ec_ser.close()
+        self.cpu_ser.close()
+        self.iter_feed_ec.join()
+        self.iter_feed_cpu.join()
+
     # Feed lines from our serial queues into the merged queue, marking when our
     # input is done.
     def iter_feed_queue(self, it):
         for i in it:
             self.serial_queue.put(i)
-        self.serial_queue.put(sentinel)
+        self.serial_queue.put(self.sentinel)
 
     # Return the next line from the queue, counting how many threads have
     # terminated and joining when done
@@ -179,6 +185,8 @@ def main():
     # power down the CPU on the device
     servo.ec_write("power off\n")
 
+    servo.close()
+
     sys.exit(retval)
 
 
diff --git a/.gitlab-ci/bare-metal/fastboot_run.py b/.gitlab-ci/bare-metal/fastboot_run.py
index 3654c7c8088..9fb2cb36b2b 100755
--- a/.gitlab-ci/bare-metal/fastboot_run.py
+++ b/.gitlab-ci/bare-metal/fastboot_run.py
@@ -36,6 +36,9 @@ class FastbootRun:
         self.ser = SerialBuffer(args.dev, "results/serial-output.txt", "R SERIAL> ", timeout=600)
         self.fastboot="fastboot boot -s {ser} artifacts/fastboot.img".format(ser=args.fbserial)
 
+    def close(self):
+        self.ser.close()
+
     def print_error(self, message):
         RED = '\033[0;31m'
         NO_COLOR = '\033[0m'
@@ -111,6 +114,7 @@ def main():
 
     while True:
         retval = fastboot.run()
+        fastboot.close()
         if retval != 2:
             break
 
diff --git a/.gitlab-ci/bare-metal/serial_buffer.py b/.gitlab-ci/bare-metal/serial_buffer.py
index 70f37709752..28565ebf4df 100755
--- a/.gitlab-ci/bare-metal/serial_buffer.py
+++ b/.gitlab-ci/bare-metal/serial_buffer.py
@@ -39,12 +39,14 @@ class SerialBuffer:
             self.serial = serial.Serial(dev, 115200, timeout=timeout if timeout else 10)
         else:
             self.f = open(filename, "rb")
+            self.serial = None
 
         self.byte_queue = queue.Queue()
         self.line_queue = queue.Queue()
         self.prefix = prefix
         self.timeout = timeout
         self.sentinel = object()
+        self.closing = False
 
         if self.dev:
             self.read_thread = threading.Thread(
@@ -58,6 +60,13 @@ class SerialBuffer:
             target=self.serial_lines_thread_loop, daemon=True)
         self.lines_thread.start()
 
+    def close(self):
+        self.closing = True
+        if self.serial:
+            self.serial.close()
+        self.read_thread.join()
+        self.lines_thread.join()
+
     # Thread that just reads the bytes from the serial device to try to keep from
     # buffer overflowing it. If nothing is received in 1 minute, it finalizes.
     def serial_read_thread_loop(self):
@@ -83,12 +92,13 @@ class SerialBuffer:
         greet = "Serial thread reading from %s\n" % self.filename
         self.byte_queue.put(greet.encode())
 
-        while True:
+        while not self.closing:
             line = self.f.readline()
             if line:
                 self.byte_queue.put(line)
             else:
                 time.sleep(0.1)
+        self.byte_queue.put(self.sentinel)
 
     # Thread that processes the stream of bytes to 1) log to stdout, 2) log to
     # file, 3) add to the queue of lines to be read by program logic