diff --git a/cpp/palettes/tones.cc b/cpp/palettes/tones.cc
index 7b42646d..37a86392 100644
--- a/cpp/palettes/tones.cc
+++ b/cpp/palettes/tones.cc
@@ -16,6 +16,7 @@
 
 #include "cpp/palettes/tones.h"
 
+#include <cmath>
 #include "cpp/cam/cam.h"
 #include "cpp/cam/hct.h"