Large vision-language models hallucinate in part because they over-rely on the language model backbone, which introduces bias from language priors and leaves insufficient attention on the visual input. This paper mitigates that over-reliance through preference learning, proposing Vision-guided Direct Preference Optimization (V-DPO) to strengthen visual context learning at training time. Evaluated on a synthetic dataset containing both response-contrast and image-contrast preference pairs, V-DPO improves over baseline methods across hallucination benchmarks and gains the most from image-contrast data.