High-frequency attenuation can reduce the rate of learned image codecs but also remove object boundaries and fine detail. We propose Semantic-Guided Adaptive Latent-Frequency Modulation (SG-AFM), which uses a semantic structural prior to guide attenuation of encoder latents. SG-AFM applies a Haar wavelet transform and combines a fixed semantic-frequency multiplier with a bounded learned correction to modulate high-frequency subbands. The semantic prior is computed only at the encoder. No semantic map is transmitted, and no decoder modules are added. Across six datasets, SG-AFM reduces PSNR-based BD-rate relative to TCM by an average of 13.17%. It achieves the best BD-rate among the compared methods on ExDark, NightCity, and OnePlus, with a mean reduction of 16.80%. An ablation on OnePlus demonstrates the benefit of spatially aligned semantic guidance, and visual comparisons illustrate improved reconstruction of local structures.

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