\renewcommand\AMC@shape@oval[5]{%
  \AMC@tracebox{#3}{#4}{\begin{tikzpicture}%
      \useasboundingbox (-0.5\AMC@boxedwidth,0.5\AMC@boxedheight)
      rectangle (0.5\AMC@boxedwidth,-0.5\AMC@boxedheight);
      \draw[#1,fill=#2,line width=\AMC@boxedrule, rounded corners=.5\AMC@boxedwidth]
      (-0.5\AMC@boxedwidth,0.5\AMC@boxedheight)
      rectangle (0.5\AMC@boxedwidth,-0.5\AMC@boxedheight);
      \draw[#1] (0,0) node {#5};
    \end{tikzpicture}}%
}
