diff --git a/supervisor/compat.py b/supervisor/compat.py
index 004c00e0f..82752b2a6 100644
--- a/supervisor/compat.py
+++ b/supervisor/compat.py
@@ -15,13 +15,13 @@ def as_bytes(s, encoding='utf-8'):
         if isinstance(s, str):
             return s
         else:
-            return s.encode(encoding)
+            return s.encode(encoding, errors='replace')
 
     def as_string(s, encoding='utf-8'):
         if isinstance(s, unicode):
             return s
         else:
-            return s.decode(encoding)
+            return s.decode(encoding, errors='replace')
 
     def is_text_stream(stream):
         try:
@@ -51,13 +51,13 @@ def as_bytes(s, encoding='utf8'):
         if isinstance(s, bytes):
             return s
         else:
-            return s.encode(encoding)
+            return s.encode(encoding, errors='replace')
 
     def as_string(s, encoding='utf8'):
         if isinstance(s, str):
             return s
         else:
-            return s.decode(encoding)
+            return s.decode(encoding, errors='replace')
 
     def is_text_stream(stream):
         import _io
diff --git a/supervisor/tests/test_compat.py b/supervisor/tests/test_compat.py
new file mode 100644
index 000000000..99f735abf
--- /dev/null
+++ b/supervisor/tests/test_compat.py
@@ -0,0 +1,35 @@
+"""Test suite for supervisor.compat"""
+
+import unittest
+
+from supervisor.compat import as_bytes, as_string
+
+
+class AsStringTests(unittest.TestCase):
+    def test_decodes_valid_utf8(self):
+        self.assertEqual(as_string(b'hello'), 'hello')
+
+    def test_returns_string_unchanged(self):
+        self.assertEqual(as_string('hello'), 'hello')
+
+    def test_replaces_invalid_bytes_instead_of_raising(self):
+        # Incomplete multi-byte sequence (e.g. truncated Korean character)
+        broken = b'\xec\x95'  # incomplete 3-byte UTF-8 sequence
+        result = as_string(broken)
+        self.assertIn('�', result)
+
+    def test_decodes_korean_utf8(self):
+        korean = '안녕하세요'.encode('utf-8')
+        self.assertEqual(as_string(korean), '안녕하세요')
+
+
+class AsBytesTests(unittest.TestCase):
+    def test_encodes_valid_string(self):
+        self.assertEqual(as_bytes('hello'), b'hello')
+
+    def test_returns_bytes_unchanged(self):
+        self.assertEqual(as_bytes(b'hello'), b'hello')
+
+    def test_encodes_korean_string(self):
+        result = as_bytes('안녕하세요')
+        self.assertEqual(result, '안녕하세요'.encode('utf-8'))