diff --git a/acinclude.m4 b/acinclude.m4
index 5e59b153ab75eaf293c3b6425425b6ebf9b1221a..f270888fb08572132a0546ae801f45e9dab70f15 100644
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -298,6 +298,9 @@ AC_DEFUN([CURL_FUNC_GETNAMEINFO_ARGTYPES], [
   ])
   if test "$curl_cv_func_getnameinfo_args" = "unknown"; then
     AC_MSG_WARN([Cannot find proper types to use for getnameinfo args])
+    AC_MSG_WARN([Undefining HAVE_GETNAMEINFO])
+    undefine([HAVE_GETNAMEINFO])dnl
+    ac_cv_func_getnameinfo="no"
   else
     gni_prev_IFS=$IFS; IFS=','
     set dummy `echo "$curl_cv_func_getnameinfo_args" | sed 's/\*/\*/g'`
diff --git a/ares/acinclude.m4 b/ares/acinclude.m4
index bf1c7de4217b6e000b67b9ef37ef5618d5c8a8ce..ac8f838088b62ec73f1be4736982063bad99f9a8 100644
--- a/ares/acinclude.m4
+++ b/ares/acinclude.m4
@@ -277,6 +277,9 @@ AC_DEFUN([CURL_FUNC_GETNAMEINFO_ARGTYPES], [
   ])
   if test "$curl_cv_func_getnameinfo_args" = "unknown"; then
     AC_MSG_WARN([Cannot find proper types to use for getnameinfo args])
+    AC_MSG_WARN([Undefining HAVE_GETNAMEINFO])
+    undefine([HAVE_GETNAMEINFO])dnl
+    ac_cv_func_getnameinfo="no"
   else
     gni_prev_IFS=$IFS; IFS=','
     set dummy `echo "$curl_cv_func_getnameinfo_args" | sed 's/\*/\*/g'`