diff --git a/progs/demos/isosurf.c b/progs/demos/isosurf.c
index dd5696507bb..d9e50a3c19d 100644
--- a/progs/demos/isosurf.c
+++ b/progs/demos/isosurf.c
@@ -27,7 +27,6 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
-#include <string.h>
 #include <math.h>
 #ifdef _WIN32
 #include <windows.h>