diff --git a/m4/curl-sysconfig.m4 b/m4/curl-sysconfig.m4
index 9b287bc762..f92fc18997 100644
--- a/m4/curl-sysconfig.m4
+++ b/m4/curl-sysconfig.m4
@@ -28,6 +28,7 @@ case $host_os in
   darwin*)
     AC_COMPILE_IFELSE([
       AC_LANG_PROGRAM([[
+#include <sys/types.h>
 #include <TargetConditionals.h>
       ]],[[
 #if TARGET_OS_MAC && !(defined(TARGET_OS_IPHONE) && TARGET_OS_IPHONE)