Abstract Rock Glacier Velocity is an Essential Climate Variable Permafrost Quantity, providing a quantifiable indicator of mountain permafrost evolution. Despite its wide usage, multi‐temporal InSAR often substantially underestimates rock glacier velocities compared to ground‐based measurements, limiting its reliability. In this study, we identified ubiquitous unwrapping errors in Sentinel‐1 interferograms as the dominant source of underestimation over 17 rock glaciers in the European Alps. To address this issue, we developed a method combining manual correction for short‐span interferograms and phase‐closure‐based correction for long‐span interferograms. Our method substantially mitigated velocity underestimation for the rock glacier Grosses Gufer, increasing the maximum velocity from ∼0.5 to ∼2.5 m/yr and achieving strong agreement with independent GNSS data (R2=0.79 ${R}^{2}=0.79$, p<0.01 $p< 0.01$) for velocities ≤2.5m/yr ${le} 2.5,text{m/yr}$. This approach provides an important step toward reliable construction of Rock Glacier Velocity time series using InSAR, enhancing its application in alpine permafrost studies.