diff --git a/passerelle/utils/json.py b/passerelle/utils/json.py
index 7b8c9401..597d9e1b 100644
--- a/passerelle/utils/json.py
+++ b/passerelle/utils/json.py
@@ -29,6 +29,7 @@
 # You should have received a copy of the GNU Affero General Public License
 # along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
+import re
 
 from passerelle.utils.validation import is_number
 
@@ -49,10 +50,22 @@ def unflatten(d, separator=FLATTEN_SEPARATOR):
 
     # ok d is a dict
 
-    def map_digits(l):
-        return [int(x) if is_number(x) else x for x in l]
+    def split_key(key):
+        def map_key(x):
+            if is_number(x):
+                return int(x)
+            elif isinstance(x, str):
+                return x.replace('%s%s' % (FLATTEN_SEPARATOR, FLATTEN_SEPARATOR), FLATTEN_SEPARATOR)
+            return x
 
-    keys = [(map_digits(key.split(separator)), key) for key in d]
+        return [
+            map_key(x)
+            for x in re.split(
+                r'(?<!%s)%s(?!%s)' % (FLATTEN_SEPARATOR, FLATTEN_SEPARATOR, FLATTEN_SEPARATOR), key
+            )
+        ]
+
+    keys = [(split_key(key), key) for key in d]
     keys.sort()
 
     def set_path(path, orig_key, d, value, i=0):
diff --git a/tests/test_utils_json.py b/tests/test_utils_json.py
index fb6a8e93..7922e463 100644
--- a/tests/test_utils_json.py
+++ b/tests/test_utils_json.py
@@ -63,6 +63,19 @@ def test_unflatten_dict():
         }
     }
 
+    assert unflatten(
+        {
+            'a' + SEP + SEP + 'b': 1,
+        }
+    ) == {'a' + SEP + 'b': 1}
+
+    assert unflatten(
+        {
+            'a' + SEP + SEP + 'b': 1,
+            'a' + SEP + SEP + 'c' + SEP + 'd': 1,
+        }
+    ) == {'a' + SEP + 'b': 1, 'a' + SEP + 'c': {'d': 1}}
+
 
 def test_unflatten_array():
     assert unflatten(
@@ -74,6 +87,13 @@ def test_unflatten_array():
         }
     ) == [{'b': [1, True]}, {'c': [[1], 'a']}]
 
+    assert unflatten(
+        {
+            '0' + SEP + 'b' + SEP + '0': 1,
+            '1' + SEP + 'c' + SEP + SEP + '0': 1,
+        }
+    ) == [{'b': [1]}, {'c' + SEP + '0': 1}]
+
 
 def test_unflatten_missing_final_index():
     with pytest.raises(ValueError) as exc_info: