diff --git a/src/openalpr/utility.cpp b/src/openalpr/utility.cpp
index 2e5f264..7aea759 100644
--- a/src/openalpr/utility.cpp
+++ b/src/openalpr/utility.cpp
@@ -18,6 +18,7 @@
 */
 
 #include <opencv2/core/core.hpp>
+#include <functional>
 
 #include "utility.h"