--- tenacity-git-7fbb876f4.old/src/effects/Compressor2.cpp
+++ tenacity-git-7fbb876f4/src/effects/Compressor2.cpp
@@ -1138,7 +1138,7 @@
 
    // envDB can become NaN is env is exactly zero.
    // As solution, use a very low dB value to prevent NaN propagation.
-   if(isnan(envDB))
+   if(std::isnan(envDB))
       envDB = -200;
 
    kneeCond = 2.0 * (envDB - mThresholdDB);