diff --git a/luametalatex-back-pdf.lua b/luametalatex-back-pdf.lua
index 2efb35c..8e2a902 100644
--- a/luametalatex-back-pdf.lua
+++ b/luametalatex-back-pdf.lua
@@ -5,6 +5,7 @@ local writer = require'luametalatex-nodewriter'
 local newpdf = require'luametalatex-pdf'
 local nametree = require'luametalatex-pdf-nametree'
 local build_fontdir = require'luametalatex-pdf-font'
+local fontmap = require'luametalatex-pdf-font-map'
 
 local utils = require'luametalatex-pdf-utils'
 local strip_floats = utils.strip_floats
@@ -744,6 +745,8 @@ token.luacmd("pdfextension", function(_, imm)
       error[[Unsupported dest type]]
     end
     node.write(whatsit)
+  elseif token.scan_keyword'mapline' then
+    fontmap.mapline(token.scan_string())
   else
   -- The following error message gobbles the next word as a side effect.
   -- This is intentional to make error-recovery easier.
diff --git a/luametalatex-bit32.lua b/luametalatex-bit32.lua
index 42dac55..b63a159 100644
--- a/luametalatex-bit32.lua
+++ b/luametalatex-bit32.lua
@@ -16,6 +16,6 @@ return {
     return (i ^ j) & mask32
   end,
   extract = function(v, shift, count)
-    return ((bit32 & v) >> shift) & ((1<<count)-1)
+    return ((mask32 & v) >> shift) & ((1<<count)-1)
   end,
 }
diff --git a/luametalatex-font-resolve.lua b/luametalatex-font-resolve.lua
index 08b53da..48aeb83 100644
--- a/luametalatex-font-resolve.lua
+++ b/luametalatex-font-resolve.lua
@@ -5,6 +5,7 @@ local fontmap = require'luametalatex-pdf-font-map'.fontmap
 local callback_find = callback.find
 
 local old_font_define = font.define
+local old_addcharacters = font.addcharacters
 
 require'luametalatex-pdf-font-map'.mapfile(kpse.find_file('pdftex.map', 'map', true))
 
@@ -110,3 +111,57 @@ function font.define(f)
   end
   return id
 end
+
+function font.addcharacters(fid, newdir)
+  old_addcharacters(fid, newdir) -- The easy part, the remaining stuff gets crazy
+  local fontdir = assert(all_fonts[fid], 'addcharacters expects an existing font')
+  local fonts_map
+  if newdir.fonts then -- FIXME: Handle default fonts table
+    if fontdir.fonts then
+      fonts_map = {}
+      for i,f in next, newdir.fonts do
+        if not f.id then
+          f.id = assert(callback_find'define_font'(f.name, f.size or -1000))
+        elseif f.id == 0 then
+          f.id = fid
+        end
+        for j,ff in next, fontdir.fonts do
+          if ff.id == f.id then
+            fonts_map[i] = j
+            goto FONT_MAPPING_SET -- A typical for ... do ... else ... end implemented using goto.
+          end
+        end
+        -- NOT FOUND, so add it
+        local new_f = #fontdir.fonts + 1
+        fontdir.fonts[new_f] = f
+        fonts_map[i] = f
+        ::FONT_MAPPING_SET::
+      end
+    else
+      fontdir.fonts = newdir.fonts
+    end
+  end
+  for cp, glyph in next, newdir do
+    local existing = fontdir[cp]
+    if existing ~= glyph then
+      if existing then
+        texio.write_nl'Overwriting existing character. Here be dragons'
+      end
+    end
+    if glyph.commands then
+      local font_seen
+      for _, cmd in ipairs(glyph.commands) do
+        if cmd[1] == 'font' then
+          font_seen = true
+          cmd[2] = fonts_map[cmd[2]]
+        elseif cmd[1] == 'slot' then
+          font_seen = true
+          cmd[2] = fonts_map[cmd[2]]
+        elseif not font_seen and cmd[1] == 'char' then
+          font_seen = true
+          cmd[1], cmd[2], cmd[3] = 'slot', fonts_map[1], cmd[2]
+        end
+      end
+    end
+  end
+end
diff --git a/luametalatex-init.lua b/luametalatex-init.lua
index 1d0c1e6..f25436b 100644
--- a/luametalatex-init.lua
+++ b/luametalatex-init.lua
@@ -23,6 +23,7 @@ do
       end
     end
   end
+  os.arg0 = arg0
   kpse.set_program_name(arg0, progname)
 end
 package.searchers[2] = function(modname)
diff --git a/luametalatex-nodewriter.lua b/luametalatex-nodewriter.lua
index a5f3222..1ce3e93 100644
--- a/luametalatex-nodewriter.lua
+++ b/luametalatex-nodewriter.lua
@@ -394,9 +394,10 @@ local function do_commands(p, c, f, fid, x, y, outer, ...)
       x = x + getwidth(n)
       direct.free(n)
     elseif cmd[1] == "slot" then
+      current_font = assert(fonts[cmd[2]], "invalid font requested")
       local n = direct.new'glyph'
       setsubtype(n, 256)
-      setfont(n, cmd[2], cmd[3])
+      setfont(n, current_font.id, cmd[2])
       nodehandler.glyph(p, n, x, y, outer, ...)
       direct.free(n)
       x = x + getwidth(n)