Command \* already defined

I have included the package amsmath as required to defined a new theorem/corollary (without number), but I keep having the following error:

! LaTeX Error: Command \* already defined.

Now, these are the packages I am including, if that can help:

\usepackage{fullpage} \usepackage{parskip} \usepackage{color} \usepackage{amsfonts} \usepackage{graphicx} \usepackage{amssymb} \usepackage{amsmath} \newtheorem*{corollary}{Corollary} 

And then I am tring to use the new command with:

\begin{corollary} ... \end{corollary}