The weir at Winznau was built as part of the Niedergösgen hydroelectric power plant on the Aare river in 1913–1917. As part of the new concession from 2027 on, a verification of earthquake safety for a seismic excitation with a return period of 5000 years was required. The maximum horizontal spectral acceleration of the elastic response spectrum of the design earthquake rose from zero at the time of planning in 1913 to almost 70% g today. A seismic analysis using the equivalent lateral force method showed that the weir pillars would topple under the seismic action, so a new construction project as replacement for the existing weir was developed and approved by the supervisory authority. At the suggestion of the Solothurn Heritage Protection Association, a second opinion on earthquake safety was obtained in order to clarify in more detail the possibilities of preserving the historical weir. A detailed, more advanced deformation-based analysis using the pushover method showed that the requirements for earthquake safety are fully met in the existing state. The seismic verification method made the crucial difference. Common, highly simplified methods often show insufficient earthquake safety and, as a consequence, lead to unnecessary retrofitting measures or even to the demolition and replacement of the structure. With more sophisticated and more demanding verification methods, the retrofitting measures can be reduced to a minimum or, as in this case, even dispensed with altogether.