diff --git a/vim/after/syntax/c.vim b/vim/after/syntax/c.vim
new file mode 100644
index 0000000..87791fb
--- /dev/null
+++ b/vim/after/syntax/c.vim
@@ -0,0 +1,23 @@
+" ADAM C vim syntax after extensions
+
+syn match cNamedConstant  "\<[A-Z_][A-Z_0-9]*\>"
+syn match cDebug          "\<DEBUG[_0-9A-Z]*\>"
+syn keyword cDebug        SKIP DOIT
+
+" Define the default highlighting.
+" For version 5.7 and earlier: only when not done already
+" For version 5.8 and later: only when an item doesn't have highlighting yet
+if version >= 508 || !exists("did_c_syn_inits")
+  if version < 508
+    let did_c_syn_inits = 1
+    command -nargs=+ HiLink hi link <args>
+  else
+    command -nargs=+ HiLink hi def link <args>
+  endif
+
+  HiLink cNamedConstant  NamedConstant
+  HiLink cDebug          Debug
+
+  delcommand HiLink
+endif
+