diff --git a/runtime/doc/syntax.txt b/runtime/doc/syntax.txt
index 29a12396d4af6f..83a18f2844580a 100644
--- a/runtime/doc/syntax.txt
+++ b/runtime/doc/syntax.txt
@@ -1021,6 +1021,7 @@ Variable		Highlight ~
 *c_no_cformat*		don't highlight %-formats in strings
 *c_no_c99*		don't highlight C99 standard items
 *c_no_c11*		don't highlight C11 standard items
+*c_no_c23*		don't highlight C23 standard items
 *c_no_bsd*		don't highlight BSD specific types
 
 When 'foldmethod' is set to "syntax" then /* */ comments and { } blocks will
diff --git a/runtime/syntax/c.vim b/runtime/syntax/c.vim
index 4d608fc4a440c0..969fe02fb8a40a 100644
--- a/runtime/syntax/c.vim
+++ b/runtime/syntax/c.vim
@@ -111,6 +111,21 @@ if (s:ft ==# "c" && !exists("c_no_c11")) || (s:in_cpp_family && !exists("cpp_no_
   syn match	cSpecialCharacter display "[Uu]'\\x\x\+'"
 endif
 
+" TODO: c_no_c23 should default to false when C23 is widely accepted
+if (s:ft ==# "c" && !get(g:, "c_no_c23", v:true)) || (s:in_cpp_family && !exists("cpp_no_cpp17"))
+  syn match	cCharacter	"u8'[^\\]'"
+  syn match	cCharacter	"u8'[^']*'" contains=cSpecial
+  if exists("c_gnu")
+    syn match	cSpecialError	"u8'\\[^'\"?\\abefnrtv]'"
+    syn match	cSpecialCharacter "u8'\\['\"?\\abefnrtv]'"
+  else
+    syn match	cSpecialError	"u8'\\[^'\"?\\abfnrtv]'"
+    syn match	cSpecialCharacter "u8'\\['\"?\\abfnrtv]'"
+  endif
+  syn match	cSpecialCharacter display "u8'\\\o\{1,3}'"
+  syn match	cSpecialCharacter display "u8'\\x\x\+'"
+endif
+
 "when wanted, highlight trailing white space
 if exists("c_space_errors")
   if !exists("c_no_trail_space_error")
@@ -277,7 +292,7 @@ if !exists("c_no_c99") " ISO C99
   syn keyword	cType		intptr_t uintptr_t
   syn keyword	cType		intmax_t uintmax_t
 endif
-if !get(g:, "c_no_c23", v:true) " FIXME: default to false when C23 is widely accepted
+if !get(g:, "c_no_c23", v:true)
   syn keyword	cType           _Decimal32 _Decimal64 _Decimal128
 endif
 
@@ -393,7 +408,7 @@ endif
 if !get(g:, "c_no_c23", v:true)
   syn region	cPreCondit	start="^\s*\zs\%(%:\|#\)\s*\%(el\)\=\%(if\|ifdef\|ifndef\)\>" skip="\\$" end="$" keepend contains=cComment,cCommentL,cCppString,cCharacter,cCppParen,cParenError,cNumbers,cCommentError,cSpaceError
 else
-  syn region	cPreCondit	start="^\s*\zs\%(%:\|#\)\s*\%(if\|ifdef\|ifndef\|elif\)\>" skip="\\$" end="$" keepend contains=cComment,cCommentL,cCppString,cCharacter,cCppParen,cParenError,cNumbers,cCommentError,cSpaceError
+  syn region	cPreCondit	start="^\s*\zs\%(%:\|#\)\s*\%(if\|ifdef\|ifndef\|elif\)\>"    skip="\\$" end="$" keepend contains=cComment,cCommentL,cCppString,cCharacter,cCppParen,cParenError,cNumbers,cCommentError,cSpaceError
 endif
 syn match	cPreConditMatch	display "^\s*\zs\%(%:\|#\)\s*\%(else\|endif\)\>"
 if !exists("c_no_if0")