diff --git a/src/zupply.hpp b/src/zupply.hpp
index 31f7f03..5ea3661 100644
--- a/src/zupply.hpp
+++ b/src/zupply.hpp
@@ -94,6 +94,7 @@
 #include <climits>
 #include <cassert>
 #include <cstring>
+#include <cmath>
 
 
 /*!