diff --git a/bincopy.py b/bincopy.py
index c7d911d..adcc0c0 100755
--- a/bincopy.py
+++ b/bincopy.py
@@ -354,7 +354,7 @@ class Segment:
     def __init__(self, minimum_address, maximum_address, data, word_size_bytes):
         self.minimum_address = minimum_address
         self.maximum_address = maximum_address
-        self.data = data
+        self.data = bytearray(data)
         self.word_size_bytes = word_size_bytes
 
     @property
diff --git a/tests/test_bincopy.py b/tests/test_bincopy.py
index eadf292..7391bbd 100644
--- a/tests/test_bincopy.py
+++ b/tests/test_bincopy.py
@@ -1810,6 +1810,15 @@ def test_add_elf_keil(self):
         with open('tests/files/elf/keil.bin', 'rb') as fin:
             self.assertEqual(bf.as_binary(), fin.read())
 
+    def test_add_elf_modify_overwrite(self):
+        bf = bincopy.BinFile()
+        bf.add_elf_file('tests/files/elf.out')
+
+        data = b'test'
+        address = bf.minimum_address
+        bf.add_binary(data, address=address, overwrite=True)
+        self.assertEqual(data, bf.as_binary(minimum_address=address, maximum_address=address+len(data)))
+
     def test_exclude_edge_cases(self):
         binfile = bincopy.BinFile()
         binfile.add_binary(b'1234', address=10)