I read 2 configs one by one: 1: > key: > 1: 1 > 2: 2 > 3: 3 2: > key: > 1: 2 > 2: 3 > 4: 5 I specified JsonMerge for a Map<Integer, Integer> property and as a result got: {1: 1, 2: 2, 3: 3, 4: 5} But I expected: {1: 2, 2: 3, 3: 3, 4: 5} Without JsonMerge I got: {1: 2, 2: 3, 4: 5} Update: Map<String, Integer> works properly - I got expected result