diff --git a/src/libjsparser/lexer.c b/src/libjsparser/lexer.c
index a056278f9..a2e13ff53 100644
--- a/src/libjsparser/lexer.c
+++ b/src/libjsparser/lexer.c
@@ -486,6 +486,14 @@ decode_keyword (void)
       .uid = KW_RESERVED
     };
   }
+  if (current_token_equals_to ("undefined"))
+  {
+    return (token)
+    {
+      .type = TOK_UNDEFINED,
+      .uid = 0
+    };
+  }
   return empty_token;
 }
 
diff --git a/src/libjsparser/lexer.h b/src/libjsparser/lexer.h
index 51531f7b8..b71292666 100644
--- a/src/libjsparser/lexer.h
+++ b/src/libjsparser/lexer.h
@@ -131,7 +131,8 @@ typedef uint8_t token_type;
 
 #define TOK_DIV 55 // /
 #define TOK_DIV_EQ 56 // /=
-#define TOK_EMPTY 57
+#define TOK_UNDEFINED 57 // undefined
+#define TOK_EMPTY 58
 
 
 /* Represents the contents of a token.  */
diff --git a/src/libjsparser/parser.c b/src/libjsparser/parser.c
index 329dba23e..a8ff5408b 100644
--- a/src/libjsparser/parser.c
+++ b/src/libjsparser/parser.c
@@ -1221,6 +1221,12 @@ parse_primary_expression (void)
       STACK_PUSH (IDX, token_data ());
       break;
     }
+    case TOK_UNDEFINED:
+    {
+      STACK_PUSH (IDX, next_temp_name ());
+      DUMP_OPCODE_3 (assignment, ID(1), OPCODE_ARG_TYPE_SIMPLE, ECMA_SIMPLE_VALUE_UNDEFINED);
+      break;
+    }
     case TOK_NULL:
     case TOK_BOOL:
     case TOK_SMALL_INT: