diff --git a/grammar.js b/grammar.js
index 33ae72b..4eac196 100644
--- a/grammar.js
+++ b/grammar.js
@@ -1561,7 +1561,7 @@ module.exports = grammar({
         seq('\\', choice(
           /[^xu]/,
           /u[0-9a-fA-F]{4}/,
-          /u\{[0-9a-fA-F]+\}/,
+          /u\{[0-9a-fA-F_]+\}/,
           /x[0-9a-fA-F]{2}/,
         )),
         /[^\\']/,
@@ -1574,7 +1574,7 @@ module.exports = grammar({
         choice(
           /[^xu]/,
           /u[0-9a-fA-F]{4}/,
-          /u\{[0-9a-fA-F]+\}/,
+          /u\{[0-9a-fA-F_]+\}/,
           /x[0-9a-fA-F]{2}/,
         ),
       )),
diff --git a/src/grammar.json b/src/grammar.json
index f345735..f3882c6 100644
--- a/src/grammar.json
+++ b/src/grammar.json
@@ -9154,7 +9154,7 @@
                           },
                           {
                             "type": "PATTERN",
-                            "value": "u\\{[0-9a-fA-F]+\\}"
+                            "value": "u\\{[0-9a-fA-F_]+\\}"
                           },
                           {
                             "type": "PATTERN",
@@ -9204,7 +9204,7 @@
               },
               {
                 "type": "PATTERN",
-                "value": "u\\{[0-9a-fA-F]+\\}"
+                "value": "u\\{[0-9a-fA-F_]+\\}"
               },
               {
                 "type": "PATTERN",
diff --git a/src/parser.c b/src/parser.c
index 533552b..2e888a1 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -1,4 +1,4 @@
-/* Automatically @generated by tree-sitter v0.25.10 */
+/* Automatically @generated by tree-sitter v0.25.9 */
 
 #include "tree_sitter/parser.h"
 
@@ -9021,39 +9021,41 @@ static bool ts_lex(TSLexer *lexer, TSStateId state) {
       END_STATE();
     case 50:
       if (lookahead == 'u') ADVANCE(53);
-      if (lookahead == 'x') ADVANCE(64);
+      if (lookahead == 'x') ADVANCE(62);
       if (lookahead != 0) ADVANCE(161);
       END_STATE();
     case 51:
       if (lookahead == 'u') ADVANCE(54);
-      if (lookahead == 'x') ADVANCE(65);
+      if (lookahead == 'x') ADVANCE(63);
       if (lookahead != 0) ADVANCE(29);
       END_STATE();
     case 52:
       if (lookahead == 'z') ADVANCE(48);
       END_STATE();
     case 53:
-      if (lookahead == '{') ADVANCE(62);
+      if (lookahead == '{') ADVANCE(66);
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
           ('a' <= lookahead && lookahead <= 'f')) ADVANCE(60);
       END_STATE();
     case 54:
-      if (lookahead == '{') ADVANCE(63);
+      if (lookahead == '{') ADVANCE(67);
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(66);
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(64);
       END_STATE();
     case 55:
       if (lookahead == '}') ADVANCE(29);
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
+          lookahead == '_' ||
           ('a' <= lookahead && lookahead <= 'f')) ADVANCE(55);
       END_STATE();
     case 56:
       if (lookahead == '}') ADVANCE(161);
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
+          lookahead == '_' ||
           ('a' <= lookahead && lookahead <= 'f')) ADVANCE(56);
       END_STATE();
     case 57:
@@ -9073,7 +9075,7 @@ static bool ts_lex(TSLexer *lexer, TSStateId state) {
     case 60:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(64);
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(62);
       END_STATE();
     case 61:
       if (('0' <= lookahead && lookahead <= '9') ||
@@ -9083,33 +9085,35 @@ static bool ts_lex(TSLexer *lexer, TSStateId state) {
     case 62:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(56);
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(61);
       END_STATE();
     case 63:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(55);
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(59);
       END_STATE();
     case 64:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(61);
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(63);
       END_STATE();
     case 65:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(59);
+          lookahead == '_' ||
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(157);
       END_STATE();
     case 66:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(65);
+          lookahead == '_' ||
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(56);
       END_STATE();
     case 67:
       if (('0' <= lookahead && lookahead <= '9') ||
           ('A' <= lookahead && lookahead <= 'F') ||
           lookahead == '_' ||
-          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(157);
+          ('a' <= lookahead && lookahead <= 'f')) ADVANCE(55);
       END_STATE();
     case 68:
       if (('A' <= lookahead && lookahead <= 'Z') ||
@@ -9594,7 +9598,7 @@ static bool ts_lex(TSLexer *lexer, TSStateId state) {
       if (lookahead == 'i') ADVANCE(38);
       if (lookahead == 'o') ADVANCE(58);
       if (lookahead == 'u') ADVANCE(38);
-      if (lookahead == 'x') ADVANCE(67);
+      if (lookahead == 'x') ADVANCE(65);
       if (('0' <= lookahead && lookahead <= '9') ||
           lookahead == '_') ADVANCE(156);
       END_STATE();
diff --git a/test/corpus/literals.txt b/test/corpus/literals.txt
index f6fa74d..be9f890 100644
--- a/test/corpus/literals.txt
+++ b/test/corpus/literals.txt
@@ -81,6 +81,7 @@ b"foo\nbar";
 "/* foo bar */ foo bar";
 "foo\x42\x43bar";
 "foo \x42  \x43 bar";
+"\u{10__FFFF}";
 
 --------------------------------------------------------------------------------
 
@@ -123,7 +124,10 @@ b"foo\nbar";
       (escape_sequence)
       (string_content)
       (escape_sequence)
-      (string_content))))
+      (string_content)))
+  (expression_statement
+    (string_literal
+      (escape_sequence))))
 
 ================================================================================
 Raw string literals
@@ -198,6 +202,7 @@ b'x';
 '\t';
 '\xff';
 '\\';
+'\u{10__FFFF}';
 
 --------------------------------------------------------------------------------
 
@@ -214,6 +219,8 @@ b'x';
     (char_literal))
   (expression_statement
     (char_literal))
+  (expression_statement
+    (char_literal))
   (expression_statement
     (char_literal)))