Recent studies have raised concerns regarding the reconstruction of glacier mass balance using tree-ring data. The method relies on a stable relationship between both variables and summer (June-August) or melt season (May-September) temperature. However, with recent anthropogenic climate change the stability of this relationship is challenged by both, a divergence between tree-ring and temperature, as well as mass balance and temperature data. Establishing to what extent this divergence influences the reconstruction of mass balance using tree-ring data is important to assess the future viability and applicability of the method. In this paper we analyze the relationship between the Tornetrask tree-ring and Storglaciaren mass balance records, their response to climate change, and investigate changes in the relationship. We provide evidence for a sensitivity loss in the Tornetrask record and quantify its impact on the reconstruction of summer mass balance of Storglaciaren. We find that by including years post 1980, the amplitude of reconstructed variability is reduced, but it remains possible to explain the variance of the record significantly. Our results suggest that for glaciers without an extensive mass balance record the applicability of the method is challenged.