diff --git a/rest_framework/fields.py b/rest_framework/fields.py
index 562e52b22..0c54f9741 100644
--- a/rest_framework/fields.py
+++ b/rest_framework/fields.py
@@ -1681,7 +1681,7 @@ class ListField(Field):
             try:
                 result.append(self.child.run_validation(item))
             except ValidationError as e:
-                errors[idx] = e.detail
+                errors[str(idx)] = e.detail
 
         if not errors:
             return result
diff --git a/tests/test_fields.py b/tests/test_fields.py
index 9a1d04979..470d17a76 100644
--- a/tests/test_fields.py
+++ b/tests/test_fields.py
@@ -1880,7 +1880,7 @@ class TestListField(FieldValues):
     ]
     invalid_inputs = [
         ('not a list', ['Expected a list of items but got type "str".']),
-        ([1, 2, 'error', 'error'], {2: ['A valid integer is required.'], 3: ['A valid integer is required.']}),
+        ([1, 2, 'error', 'error'], {'2': ['A valid integer is required.'], '3': ['A valid integer is required.']}),
         ({'one': 'two'}, ['Expected a list of items but got type "dict".'])
     ]
     outputs = [
@@ -1916,9 +1916,9 @@ class TestNestedListField(FieldValues):
         ([[]], [[]])
     ]
     invalid_inputs = [
-        (['not a list'], {0: ['Expected a list of items but got type "str".']}),
-        ([[1, 2, 'error'], ['error']], {0: {2: ['A valid integer is required.']}, 1: {0: ['A valid integer is required.']}}),
-        ([{'one': 'two'}], {0: ['Expected a list of items but got type "dict".']})
+        (['not a list'], {'0': ['Expected a list of items but got type "str".']}),
+        ([[1, 2, 'error'], ['error']], {'0': {'2': ['A valid integer is required.']}, '1': {'0': ['A valid integer is required.']}}),
+        ([{'one': 'two'}], {'0': ['Expected a list of items but got type "dict".']})
     ]
     outputs = [
         ([[1, 2], [3]], [[1, 2], [3]]),