diff --git a/scalameta/tokenizers/shared/src/main/scala/scala/meta/internal/tokenizers/LegacyScanner.scala b/scalameta/tokenizers/shared/src/main/scala/scala/meta/internal/tokenizers/LegacyScanner.scala
index 352a71ca1b..db29ef86bc 100644
--- a/scalameta/tokenizers/shared/src/main/scala/scala/meta/internal/tokenizers/LegacyScanner.scala
+++ b/scalameta/tokenizers/shared/src/main/scala/scala/meta/internal/tokenizers/LegacyScanner.scala
@@ -233,8 +233,10 @@ class LegacyScanner(input: Input, dialect: Dialect) {
     }
 
     @inline
-    def reportIllegalCharacter(): Unit = curr
-      .setInvalidToken(s"illegal character '\\u${"%04x".format(ch)}'")
+    def reportIllegalCharacter(): Unit = {
+      val output = "\\u" + Integer.toHexString(ch | 0x10000).substring(1);
+      curr.setInvalidToken(s"illegal character '$output'")
+    }
 
     (ch: @switch) match {
       case ' ' =>