diff --git a/octoprint_bambu_printer/printer/printer_serial_io.py b/octoprint_bambu_printer/printer/printer_serial_io.py
index 35324a2..0a9e877 100644
--- a/octoprint_bambu_printer/printer/printer_serial_io.py
+++ b/octoprint_bambu_printer/printer/printer_serial_io.py
@@ -64,24 +64,25 @@ class PrinterSerialIO(threading.Thread):
                 data = to_bytes(data, encoding="ascii", errors="replace")
                 self.input_bytes.task_done()
 
-                line, buffer = self._read_next_line_buffered(data, buffer)
+                buffer += data
+                line, buffer = self._read_next_line(buffer)
                 while line is not None:
                     self._received_lines += 1
                     self._process_input_gcode_line(line)
-                    line, buffer = self._read_next_line_buffered(data, buffer)
+                    line, buffer = self._read_next_line(buffer)
             except queue.Empty:
                 continue
 
         self._log.debug("Closing IO read loop")
 
-    def _read_next_line_buffered(self, additional: bytes, buffer: bytes):
-        buffer += additional
+    def _read_next_line(self, buffer: bytes):
         new_line_pos = buffer.find(b"\n") + 1
         if new_line_pos > 0:
-            additional = buffer[:new_line_pos]
+            line = buffer[:new_line_pos]
             buffer = buffer[new_line_pos:]
-
-        return additional, buffer
+            return line, buffer
+        else:
+            return None, buffer
 
     def close(self):
         self.flush()
diff --git a/test/test_gcode_execution.py b/test/test_gcode_execution.py
index e686234..c56affd 100644
--- a/test/test_gcode_execution.py
+++ b/test/test_gcode_execution.py
@@ -96,6 +96,7 @@ def ftps_session_mock(files_info_ftp):
         ftps_session.size.side_effect = DictGetter(
             {file: info[0] for file, info in files_info_ftp.items()}
         )
+
         ftps_session.sendcmd.side_effect = DictGetter(
             {f"MDTM {file}": info[1] for file, info in files_info_ftp.items()}
         )
@@ -141,7 +142,7 @@ def test_initial_state(printer: BambuVirtualPrinter):
 
 def test_list_sd_card(printer: BambuVirtualPrinter):
     printer.write(b"M20\n")  # GCode for listing SD card
-    printer.flush()
+    printer.close()
     result = printer.readlines()
     assert result == ""  # Replace with the actual expected result