diff --git a/luametalatex-baseregisters.lua b/luametalatex-baseregisters.lua
index 2b47c16..2e84965 100644
--- a/luametalatex-baseregisters.lua
+++ b/luametalatex-baseregisters.lua
@@ -128,6 +128,7 @@ pdf_variable(dimen_code, token.scan_dimen, 'horigin', tex.sp'1in')
 pdf_variable(dimen_code, token.scan_dimen, 'vorigin', tex.sp'1in')
 pdf_variable(dimen_code, token.scan_dimen, 'linkmargin', tex.sp'0pt')
 pdf_variable(dimen_code, token.scan_dimen, 'destmargin', tex.sp'0pt')
+pdf_variable(dimen_code, token.scan_dimen, 'threadmargin', tex.sp'0pt') -- We don't support threads, so this isn't doing anything
 pdf_variable(count_code, token.scan_int, 'majorversion', 1)
 pdf_variable(count_code, token.scan_int, 'minorversion', 7)
 pdf_variable(count_code, token.scan_int, 'compresslevel', 0)
@@ -155,6 +156,14 @@ pdf_toks('pageattr', '')
 pdf_toks('pagesattr', '')
 pdf_toks('pageresources', '')
 
+-- The following two are special: The should have force_default=true because we ignore them,
+-- but they are token lists so that doesn't really work. Instead, we check during shipout that
+-- the variables are empty. TODO: Find a nicer solution
+-- The reason for not implementing them is that XForm specific resources and attributes make
+-- much more sense, so these two generic ones are useless and error-prone.
+pdf_toks('xformresources', '')
+pdf_toks('xformattr', '')
+
 function tex.getbodydir() return tex.bodydirection end
 function tex.getpagedir() return tex.pagedirection end
 function tex.setbodydir(i) tex.bodydirection = i end
diff --git a/luametalatex-pdf-savedbox.lua b/luametalatex-pdf-savedbox.lua
index dabcffe..4dad21c 100644
--- a/luametalatex-pdf-savedbox.lua
+++ b/luametalatex-pdf-savedbox.lua
@@ -1,4 +1,5 @@
 local writer -- = require'luametalatex-nodewriter' -- This would introduce some cyclic dependency
+local pdfvariable = pdf.variable
 
 -- XForms currently have the form {width, height, depth, objnum, attributes, list, margin}
 local xforms = {}
@@ -12,6 +13,9 @@ local function shipout(pfile, xform, fontdirs, usedglyphs)
   local out, resources, annots = writer(pfile, list, fontdirs, usedglyphs)
   cur_page = last_page
   assert(annots == '')
+  if pdfvariable.xformattr ~= '' or pdfvariable.xformresources ~= '' then
+    texio.write_nl('term and log', 'WARNING (savedboxresource shipout): Ignoring unsupported PDF variables xformattr and xformresources. Specify resources and attributes for specific XForms instead.')
+  end
   local dict = string.format('/Subtype/Form/BBox[%f %f %f %f]/Resources<<%s%s>>%s', -to_bp(margin), -to_bp(list.depth+margin), to_bp(list.width+margin), to_bp(list.height+margin), resources, xform.resources or '', xform.attributes or '')
   node.flush_list(list)
   xform.list = nil