diff --git a/CMake/CurlTests.c b/CMake/CurlTests.c
index 83d743d34e..483b9a218b 100644
--- a/CMake/CurlTests.c
+++ b/CMake/CurlTests.c
@@ -228,7 +228,7 @@ int main(void)
 #endif
 int main(void)
 {
-  int flags = 0;
+  unsigned long flags = 0;
   if(0 != ioctlsocket(0, FIONBIO, &flags))
     return 1;
   ;