diff --git a/core/src/main/java/org/jruby/lexer/yacc/RubyLexer.java b/core/src/main/java/org/jruby/lexer/yacc/RubyLexer.java
index fa26107..4db7e14 100644
--- a/core/src/main/java/org/jruby/lexer/yacc/RubyLexer.java
+++ b/core/src/main/java/org/jruby/lexer/yacc/RubyLexer.java
@@ -621,7 +621,7 @@ public class RubyLexer {
      * mri: is_identchar
      */
     public boolean isIdentifierChar(int c) {
-        return Character.isLetterOrDigit(c) || c == '_' || isMultiByteChar(c);
+        return encoding.isAlnum(c) || c == '_' || !Encoding.isAscii(c);
     }

     public boolean isASCII(int c) {
@@ -1768,6 +1768,20 @@ public class RubyLexer {
     }

     private int identifier(int c, boolean commandState) throws IOException {
+        ByteList aggregate = new ByteList();
+        do {
+            if (!Encoding.isAscii(c)) mb = ENC_CODERANGE_UNKNOWN;
+            if (tokenAddMBC(c, aggregate) == -1) return 0;
+            c = nextToken();
+        } while (isIdentifierChar(c));
+
+        int result = 0;
+
+        if (c == '!' || c == '?') {
+            result = Tokens.tFID;
+        } else {
+            this
+        }
         if (!isIdentifierChar(c)) {
             String badChar = "\\" + Integer.toOctalString(c & 0xff);
             throw new SyntaxException(PID.CHARACTER_BAD, getPosition(), getCurrentLine(),
@@ -1791,8 +1805,7 @@ public class RubyLexer {
         } else {
             src.unread(c);
         }
-        
-        int result = 0;
+

         last_state = lex_state;
         if (lastBangOrPredicate) {