diff --git a/snappy.cc b/snappy.cc
index 56b8c82..877b65a 100644
--- a/snappy.cc
+++ b/snappy.cc
@@ -74,6 +74,7 @@
 #include <cstdint>
 #include <cstdio>
 #include <cstring>
+#include <functional>
 #include <memory>
 #include <string>
 #include <utility>