Index: wp-includes/category-template.php
===================================================================
--- wp-includes/category-template.php	(revision 6597)
+++ wp-includes/category-template.php	(working copy)
@@ -377,7 +377,7 @@
 		$tag_link = clean_url($tag_links[$tag]);
 		$tag = str_replace(' ', ' ', wp_specialchars( $tag ));
 		$a[] = "<a href='$tag_link' class='tag-link-$tag_id' title='" . attribute_escape( sprintf( __ngettext('%d topic','%d topics',$count), $count ) ) . "'$rel style='font-size: " .
-			( $smallest + ( ( $count - $min_count ) * $font_step ) )
+			($smallest == $largest ? $smallest : ( $smallest + ( ( $count - $min_count ) * $font_step ) ) )
 			. "$unit;'>$tag</a>";
 	}