1 files changed, 1 insertions, 0 deletions
diff --git a/phpcpp.h b/phpcpp.h
index c3f3365..51ded73 100644
--- a/phpcpp.h
+++ b/phpcpp.h
@@ -22,6 +22,7 @@
 #include <exception>
 #include <map>
 #include <set>
+#include <functional>
 
 /**
  *  Include all headers files that are related to this library