OR in if statement

The OR operator in my if statement doesn't seem to be working. Here is my code

<perch:if exists="vimeo-description OR main-video-description">
  WITH DESCRIPTION
  <perch:template path="content/_project-section--with-description.html" />

  <perch:else />
  WITHOUT DESCRIPTION
  <perch:template path="content/_project-section--no-description.html" />

</perch:if>

I know for a fact that vimeo-description exists but I still get the WITHOUT DESCRIPTION version loading. The statement works if I just use vimeo-description it works, like so:

<perch:if exists="vimeo-description">
  WITH DESCRIPTION
  <perch:template path="content/_project-section--with-description.html" />

  <perch:else />
  WITHOUT DESCRIPTION
  <perch:template path="content/_project-section--no-description.html" />

</perch:if>

Is this a bug or am I doing something wrong?