Index: pym/portage.py
===================================================================
--- pym/portage.py	(revision 5884)
+++ pym/portage.py	(working copy)
@@ -4434,8 +4434,18 @@
 			for x in settings.categories:
 				if mydb.cp_list(x+"/"+myp,use_cache=use_cache):
 					matches.append(x+"/"+myp)
-		if (len(matches)>1):
-			raise ValueError, matches
+		if len(matches) > 1:
+			if len(matches) == 2:
+				for x in matches:
+					if not x.startswith("virtual/"):
+						# Assume that the non-virtual is desired.  This helps
+						# avoid the ValueError for invalid deps that come from
+						# installed packages (during reverse blocker detection,
+						# for example).
+						mykey = x
+						break
+			if mykey is None:
+				raise ValueError, matches
 		elif matches:
 			mykey=matches[0]