diff --git a/m4/xcb.m4 b/m4/xcb.m4
index cf525c0..a43082a 100644
--- a/m4/xcb.m4
+++ b/m4/xcb.m4
@@ -56,6 +56,11 @@ m4_if(xcb_defopt, [auto], [
 # This extension has a default value of "auto" and depends on the value of $2
 if test "x$BUILD_[]UP" = "xauto" ; then
     BUILD_[]UP=$2
+fi
+if test "x$BUILD_[]UP" = "xyes" ; then
+    if test "x$2" = "xno" ; then
+      AC_MSG_ERROR([Extension []UP requested, but dependencies are not met])
+    fi
 fi])
 
 m4_undefine([xcb_defopt])dnl