diff --git a/src/python_template/logger/logger.py b/src/python_template/logger/logger.py
index 2228cd2..7b6e465 100644
--- a/src/python_template/logger/logger.py
+++ b/src/python_template/logger/logger.py
@@ -154,7 +154,7 @@ class LoggerMixin:  # pylint: disable=too-few-public-methods
     _lock_logger = threading.Lock()  # Add a lock for thread safety.
     _loggers: dict = {}
 
-    def __init__(
+    def __init__(  # pylint: disable=too-many-branches,too-many-statements
         self,
         logger_filename: str | Path | None = None,
         logger_format: str | None = None,
@@ -183,6 +183,10 @@ def __init__(
             LoggerMixin._lock_logger
         ):  # Acquire the lock before making changes.
             # Get call stack info:
+            if hasattr(self, "logger"):
+                if DEBUG_PRINTS:
+                    print(f"{type(self).__name__} already has a logger.")
+                return
             stack = traceback.extract_stack()
             caller = stack[-2]  # The frame that called this __init__.
             caller_info = f"{caller.filename}:{caller.lineno} in {caller.name}"
diff --git a/tests/test_logger/test_logger.py b/tests/test_logger/test_logger.py
index 75002ee..24f7030 100644
--- a/tests/test_logger/test_logger.py
+++ b/tests/test_logger/test_logger.py
@@ -1,10 +1,11 @@
 """This file contains tests for the LoggerMixin class."""
 
 import logging
+import os
 from datetime import datetime
 from pathlib import Path
 
-# from python_template.logger import LoggerMixin
+from python_template.logger import LoggerMixin
 from python_template.logger.logger import DebugCategoryNameFilter
 
 TEST_TEXT = "Some test text."
@@ -166,3 +167,24 @@ def test_debug_category_verbosity_help(create_test_debug_category):
     assert lines[3] == level_3_text
     assert lines[4] == level_4_text
     assert lines[5] == level_5_text
+
+
+def test_logger_duplication_guard():
+    """Tests the duplication guard in LoggerMixin."""
+
+    class TestClass(LoggerMixin):  # pylint: disable=too-few-public-methods
+        """A test class that inherits LoggerMixin."""
+
+        def __init__(self):
+            super().__init__()
+            # self.old_logger = self.logger.copy()
+            self.old_logger_filename = self.logger_filename
+            LoggerMixin.__init__(self)
+
+    test_class = TestClass()
+    # assert test_class.old_logger == test_class.logger
+    assert test_class.old_logger_filename == test_class.logger_filename
+    for handler in test_class.logger.handlers:
+        handler.close()
+    if os.path.exists(test_class.logger_filename):
+        os.remove(test_class.logger_filename)