diff --git a/src/lexer.ml b/src/lexer.ml
index 6b1580b..663f518 100644
--- a/src/lexer.ml
+++ b/src/lexer.ml
@@ -146,10 +146,11 @@ let rec string lexbuf =
   | "\\\"" -> Buffer.add_char string_buffer '"'; string lexbuf
   | "\\b" -> Buffer.add_char string_buffer '\b'; string lexbuf
   | "\\f" -> Buffer.add_char string_buffer '\012'; string lexbuf
-  | "\\u{", Rep (hex_digit, 1 .. 6), '}' ->
-    (* TODO: Disallow 7+ hex digits inside \u{...}? *)
+  | "\\u{", Plus hex_digit, '}' ->
     let code_str =
       Sedlexing.Utf8.sub_lexeme lexbuf 3 (Sedlexing.lexeme_length lexbuf - 4) in
+    if String.length code_str > 6 then
+      error "Invalid unicode code point, cannot contain more than 6 hex digits";
     let code = int_of_string @@ "0x" ^ code_str in
     if code > 0x10FFFF then
       error "Invalid unicode code point, cannot be greater than 10FFFF";
diff --git a/test/parse.ml b/test/parse.ml
index 820f1f0..48b4b45 100644
--- a/test/parse.ml
+++ b/test/parse.ml
@@ -378,9 +378,8 @@ let%test_module "strings" = (module struct
     [%expect {| (- (string "a _ a _ \226\129\159")) |}]
 
   let%expect_test "\\u{...} cannot contain more than 6 hex digits" =
-    (* TODO: Raise an error instead? *)
     test {|- "\u{1234567}"|};
-    [%expect {| (- (string "\\u{1234567}")) |}]
+    [%expect {| Error: :1:4-1:15: Invalid unicode code point, cannot contain more than 6 hex digits |}]
 
   let%expect_test "\\u{...} should not accept a > 0x10FFFF code point" =
     test {|- "\u{11FBBF} _"|};