diff --git a/samples/c/smiledetect.cpp b/samples/c/smiledetect.cpp
index 63254dca8..ff032e479 100644
--- a/samples/c/smiledetect.cpp
+++ b/samples/c/smiledetect.cpp
@@ -2,6 +2,7 @@
 #include "opencv2/highgui/highgui.hpp"
 #include "opencv2/imgproc/imgproc.hpp"
 
+#include <cctype>
 #include <iostream>
 #include <iterator>
 #include <stdio.h>