diff --git a/src/expr.cpp b/src/expr.cpp
index 25c68f6..47237cb 100644
--- a/src/expr.cpp
+++ b/src/expr.cpp
@@ -19,6 +19,7 @@ namespace std {
 #include <memory.h>
 #include <stdlib.h>
 #include <string.h>
+#include <sys/types.h>
 }
 
 using namespace std;