diff --git a/src/cbor/lexer.cr b/src/cbor/lexer.cr
index 2a5c9e9..34b6906 100644
--- a/src/cbor/lexer.cr
+++ b/src/cbor/lexer.cr
@@ -19,6 +19,14 @@ class CBOR::Lexer
       Token.new(kind: Token::Kind::UInt, value: @curren_byte)
     when 0x18
       read_uint8
+    when 0x19
+      read_uint16
+    when 0x1a
+      read_uint32
+    when 0x1b
+      read_uint64
+    when .<= 0x37
+      Token.new(kind: Token::Kind::NInt, value: Int8(@curren_byte))
     end
   end
 
@@ -29,6 +37,30 @@ class CBOR::Lexer
     Token.new(kind: Token::Kind::UInt, value: byte)
   end
 
+  private def read_uint16
+    value = UInt16.from_io(read_next(2), IO::ByteFormat::BigEndian)
+    Token.new(kind: Token::Kind::UInt, value: value)
+  end
+
+  private def read_uint32
+    value = UInt32.from_io(read_next(4), IO::ByteFormat::BigEndian)
+    Token.new(kind: Token::Kind::UInt, value: value)
+  end
+
+  private def read_uint64
+    value = UInt64.from_io(read_next(8), IO::ByteFormat::BigEndian)
+    Token.new(kind: Token::Kind::UInt, value: value)
+  end
+
+  private def read_next(n : Int)
+    slice = Bytes.new(n)
+
+    read = @io.read(slice)
+    return unexpect_eof if read == 0
+
+    slice
+  end
+
   private def unexpected_eof
     raise "Unexpected EOF"
   end