diff --git a/tools/lexer/idea-flex-kotlin.skeleton b/tools/lexer/idea-flex-kotlin.skeleton
index e241f679f5ba..49882c195f9b 100644
--- a/tools/lexer/idea-flex-kotlin.skeleton
+++ b/tools/lexer/idea-flex-kotlin.skeleton
@@ -201,6 +201,17 @@ companion object {
 
   private fun charCount(codePoint: Int): Int = if (codePoint < 0x10000) 1 else 2
 
+  private fun Char.Companion.codePointBefore(seq: CharSequence, index: Int): Int {
+    var i = index - 1
+    val c2 = seq[i];
+    if (c2.isLowSurrogate() && index > 0) {
+      val c1 = seq[i - 1];
+      if (c1.isHighSurrogate()) {
+        return Char.toCodePoint(c1, c2);
+      }
+    }
+    return c2.code
+  }
 
   /**
    * Reports an error that occurred while scanning.