Index: pym/_emerge/__init__.py
===================================================================
--- pym/_emerge/__init__.py	(revision 12649)
+++ pym/_emerge/__init__.py	(working copy)
@@ -5274,23 +5274,14 @@
 		cat, atom_pn = portage.catsplit(null_cp)
 
 		dbs = self._filtered_trees[root_config.root]["dbs"]
-		cp_set = set()
+		categories = set()
 		for db, pkg_type, built, installed, db_keys in dbs:
-			cp_set.update(db.cp_all())
-		for cp in list(cp_set):
-			cat, pn = portage.catsplit(cp)
-			if pn != atom_pn:
-				cp_set.discard(cp)
+			for cat in db.categories:
+				if db.cp_list("%s/%s" % (cat, atom_pn)):
+					categories.add(cat)
+
 		deps = []
-		for cp in cp_set:
-			have_pkg = False
-			for db, pkg_type, built, installed, db_keys in dbs:
-				if db.cp_list(cp):
-					have_pkg = True
-					break
-			if not have_pkg:
-				continue
-			cat, pn = portage.catsplit(cp)
+		for cat in categories:
 			deps.append(insert_category_into_atom(
 				atom_without_category, cat))
 		return deps