Feature fusion has been proven effective [31, 32] in image search. Typically, it is assumed that the to-be-fused heterogeneous features work well by themselves for the query. However, in a more realistic situation, one does not know in advance whether a feature is effective or not for a given query. As a result, it is of great importance to identify feature effectiveness in a query-adaptive manner. Towards this goal, this paper proposes a simple yet effective late fusion method at score level. Our motivation is that the sorted score curve exhibits an" L" shape for a good feature, but descends gradually for a bad one (Fig. 1). By approximating score curve's tail with a reference collected on irrelevant data, the effectiveness of a feature can be estimated as negatively related to the area under the normalized score curve. Experiments are conducted on two image search datasets and one person re-identification dataset. We show that our method is robust to parameter changes, and outperforms two popular fusion schemes, especially on the resistance to bad features. On the three datasets, our results are competitive to the state-of-the-arts.