Index: src/cmd/unit_generic.cpp
--- src/cmd/unit_generic.cpp.orig
+++ src/cmd/unit_generic.cpp
@@ -95,6 +95,7 @@
 
 #include "unit_find.h"
 #include "pilot.h"
+#include <cmath>
 
 #include <iostream>
 #define DEBUG_MESH_ANI
