What is wrong with the following system Handler for a Textbox

What is wrong with the following: I get an error:
CS0123: No overload for 'txt1_TextChanged' matches delegate 'System.EventHandler'



protected void txt1_TextChanged(TextBox sender, EventArgs e){
}

html

<asp:TextBox ID="txt1" runat="server" OnTextChanged="txt1_TextChanged"></asp:TextBox>