diff --git a/samples/c/motempl.c b/samples/c/motempl.c
index 18e33a557..ec76696bc 100644
--- a/samples/c/motempl.c
+++ b/samples/c/motempl.c
@@ -3,6 +3,7 @@
 #include "opencv2/highgui/highgui.hpp"
 #include <time.h>
 #include <stdio.h>
+#include <ctype.h>
 
 void help()
 {