<p>Time-variable satellite gravimetry constrains global glacier mass change, but requires correction for glacial isostatic adjustment. These corrections are commonly treated as slowly varying background signals from past ice loading and assumed to be separable from present-day glacier loss. Here we show that this separation can fail in low-viscosity settings, where viscoelastic rebound can approach isostatic compensation on annual-to-decadal timescales and covary with ongoing ice retreat. Using millennium-scale glacier reconstructions and viscoelastic Earth modelling, we incorporate rapid rebound into gravimetry trend inversions for Alaska and Iceland. This reveals additional ice loss of ~7 ± 1 Gt yr⁻¹ in Alaska and ~3 ± 1 Gt yr⁻¹ in Iceland (2002–2025), with uncertainties spanning Earth-model spread. Globally, gravimetry-inferred glacier mass loss increases by ~10 Gt yr⁻¹ (~0.03 mm yr⁻¹ global mean sea-level rise; ~4%), with ~9% more loss in Alaska and about one-third more in Iceland. Similar inversion biases are expected elsewhere in low-viscosity regions.</p>