diff --git a/fairseq/data/dictionary.py b/fairseq/data/dictionary.py
index 7ad590a19b..03df789f7e 100644
--- a/fairseq/data/dictionary.py
+++ b/fairseq/data/dictionary.py
@@ -124,9 +124,9 @@ def unk_string(self, escape=False):
         else:
             return self.unk_word
 
-    def add_symbol(self, word, n=1, overwrite=False):
+    def add_symbol(self, word, n=1, overwrite=True):
         """Adds a word to the dictionary"""
-        if word in self.indices and not overwrite:
+        if word in self.indices and overwrite:
             idx = self.indices[word]
             self.count[idx] = self.count[idx] + n
             return idx
@@ -218,11 +218,17 @@ def unk(self):
     def load(cls, f, add_special_symbols=True):
         """Loads the dictionary from a text file with the format:
 
-        ```
-        <symbol0> <count0>
-        <symbol1> <count1>
-        ...
-        ```
+        Example::
+            ```
+            <symbol0> <count0> [<flag0>]
+            <symbol1> <count1> [<flag1>]
+            ...
+            ```
+        
+        Note:
+            Possible flags are `#fairseq:overwrite` to overwrite duplicates 
+            and `#fairseq:duplicate` to keep them (for backward compatibility 
+            after bug fix)
         """
         d = cls(add_special_symbols=add_special_symbols)
         d.add_from_file(f)
@@ -255,31 +261,36 @@ def add_from_file(self, f):
                 if field == "#fairseq:overwrite":
                     overwrite = True
                     line, field = line.rsplit(" ", 1)
-                else:
+                elif field == "#fairseq:duplicate":
                     overwrite = False
+                    line, field = line.rsplit(" ", 1)
+                else:
+                    if line in self:
+                        raise RuntimeError(
+                            "Duplicate word found when loading Dictionary: '{}'. "
+                            "Duplicate words can overwrite earlier ones by adding the "
+                            "#fairseq:overwrite flag at the end of the corresponding row "
+                            "in the dictionary file. Use the #fairseq:duplicate flag "
+                            "to keep duplicates in the dictionary (backward compatibility "
+                            "after bug fix). If using the Camembert model, please "
+                            "download an updated copy of the model file.".format(word)
+                        )
+                    overwrite = True # default behaviour
                 count = int(field)
                 word = line
-                if word in self and not overwrite:
-                    raise RuntimeError(
-                        "Duplicate word found when loading Dictionary: '{}'. "
-                        "Duplicate words can overwrite earlier ones by adding the "
-                        "#fairseq:overwrite flag at the end of the corresponding row "
-                        "in the dictionary file. If using the Camembert model, please "
-                        "download an updated copy of the model file.".format(word)
-                    )
                 self.add_symbol(word, n=count, overwrite=overwrite)
             except ValueError:
                 raise ValueError(
                     f"Incorrect dictionary format, expected '<token> <cnt> [flags]': \"{line}\""
                 )
 
-    def _save(self, f, kv_iterator):
+    def _save(self, f, kvf_iterator):
         if isinstance(f, str):
             PathManager.mkdirs(os.path.dirname(f))
             with PathManager.open(f, "w", encoding="utf-8") as fd:
                 return self.save(fd)
-        for k, v in kv_iterator:
-            print("{} {}".format(k, v), file=f)
+        for k, v, flag in kvf_iterator:
+            print("{} {} {}".format(k, v, flag), file=f)
 
     def _get_meta(self):
         return [], []
@@ -295,6 +306,12 @@ def save(self, f):
             zip(
                 ex_keys + self.symbols[self.nspecial :],
                 ex_vals + self.count[self.nspecial :],
+                [ 
+                    '#fairseq:duplicate' 
+                    if s in self.symbols[:self.nspecial+i] 
+                    else '' 
+                    for i, s in enumerate(self.symbols[self.nspecial:]) 
+                ]
             ),
         )
 
diff --git a/tests/test_dictionary.py b/tests/test_dictionary.py
index dc9d71b3c7..8f367e8ab3 100644
--- a/tests/test_dictionary.py
+++ b/tests/test_dictionary.py
@@ -78,7 +78,6 @@ def assertMatch(ids, ref_ids):
             assertMatch(finalized_ids, reload_ids)
 
     def test_overwrite(self):
-        # for example, Camembert overwrites <unk>, <s> and </s>
         dict_file = io.StringIO(
             "<unk> 999 #fairseq:overwrite\n"
             "<s> 999 #fairseq:overwrite\n"
@@ -88,6 +87,33 @@ def test_overwrite(self):
         )
         d = Dictionary()
         d.add_from_file(dict_file)
+        self.assertEqual(d.bos(), 0)
+        self.assertEqual(d.pad(), 1)
+        self.assertEqual(d.eos(), 2)
+        self.assertEqual(d.unk(), 3)
+        self.assertEqual(d.index("<pad>"), 1)
+        self.assertEqual(d.index("foo"), 3)
+        self.assertEqual(d.index("<unk>"), 3)
+        self.assertEqual(d.index("<s>"), 0)
+        self.assertEqual(d.index("</s>"), 2)
+        self.assertEqual(d.index(","), 4)
+        self.assertEqual(d.index("▁de"), 5)
+    
+    def test_duplicate(self):
+        # for example, Camembert duplicates <unk>, <s> and </s>
+        dict_file = io.StringIO(
+            "<unk> 999 #fairseq:duplicate\n"
+            "<s> 999 #fairseq:duplicate\n"
+            "</s> 999 #fairseq:duplicate\n"
+            ", 999\n"
+            "▁de 999\n"
+        )
+        d = Dictionary()
+        d.add_from_file(dict_file)
+        self.assertEqual(d.bos(), 0)
+        self.assertEqual(d.pad(), 1)
+        self.assertEqual(d.eos(), 2)
+        self.assertEqual(d.unk(), 3)
         self.assertEqual(d.index("<pad>"), 1)
         self.assertEqual(d.index("foo"), 3)
         self.assertEqual(d.index("<unk>"), 4)
@@ -96,8 +122,8 @@ def test_overwrite(self):
         self.assertEqual(d.index(","), 7)
         self.assertEqual(d.index("▁de"), 8)
 
-    def test_no_overwrite(self):
-        # for example, Camembert overwrites <unk>, <s> and </s>
+    def test_no_overwrite_nor_duplicate(self):
+        # for example, Camembert duplicates <unk>, <s> and </s>
         dict_file = io.StringIO(
             "<unk> 999\n" "<s> 999\n" "</s> 999\n" ", 999\n" "▁de 999\n"
         )