functions.php conditional tag – only show in single.php?

//Geo Map
add_action( 'woo_post_inside_after', 'my_geo_mashup' );
function my_geo_mashup() {
    global $post;
if ( in_category('listings') ) {
        echo GeoMashup::map();
       }
}

Works to embed my map tag only on my single posts categorized as “listings”
But, the embedded tag is also showing within the index of posts (thumb, title, meta, excerpt) and I need to remove it from the loop of posts and have it only show on the single.php

thoughts?