diff -ur a/include/gestures/include/finger_metrics.h b/include/gestures/include/finger_metrics.h
--- a/include/gestures/include/finger_metrics.h    1970-01-01 09:00:01.000000000 +0900
+++ b/include/gestures/include/finger_metrics.h    2018-12-01 16:58:51.590718511 +0900
@@ -5,6 +5,8 @@
 #ifndef GESTURES_FINGER_METRICS_H_
 #define GESTURES_FINGER_METRICS_H_
 
+#include <math.h>
+
 #include "gestures/include/gestures.h"
 #include "gestures/include/prop_registry.h"
#include "gestures/include/vector.h"