diff --git a/m4/needtrio.m4 b/m4/needtrio.m4
index 45478f9..7439cd1 100644
--- a/m4/needtrio.m4
+++ b/m4/needtrio.m4
@@ -9,6 +9,7 @@ AC_DEFUN([LFTP_NEED_TRIO],[
       else
 
       AC_RUN_IFELSE([AC_LANG_SOURCE([[
+         #include <stdio.h>
 	 int main()
 	 {
 	    unsigned long long x=0,x1;