--- a/modules/geoipbackend/geoipbackend.cc
+++ b/modules/geoipbackend/geoipbackend.cc
@@ -26,6 +26,7 @@
 #include "geoipinterface.hh"
 #include "pdns/dns_random.hh"
 #include <sstream>
+#include <cmath>
 #include <regex.h>
 #include <glob.h>
 #include <boost/algorithm/string/replace.hpp>