  Based on photometric data obtained between 1935 and 2017, $O-C$ diagrams were
built for 22 RR Lyrae stars in the globular cluster NGC 6171, leading to the
discovery of secular period changes in 4 variables for which we have calculated
their period change rates $\beta$. In contrast we find that $82\%$ of the
sample stars have stable periods over the last 82 years. For the stable period
stars, the whole data base has been employed to refine their periods. Among the
period changing stars, three (V10, V12 and V16) have decreasing periods larger
than expected from stellar evolution. Despite these individual cases of
significant period change rate, the golbal average of the measured period
changes in the cluster is basically zero, in consonance with theoretical
predictions for clusters with redder horizontal branches. The hitherto
unpublished observations, now brought into public domain, are employed to
calculate a set of times of maximum light which are used in the present
analysis.
