diff --git a/htools/Ganeti/HTools/Graph.hs b/htools/Ganeti/HTools/Graph.hs
index a5616ecd2304cbd71e1022fd5d45aae41e6e3d68..1fa350094b0a07dd2691bb26abb9afd1ebd8c896 100644
--- a/htools/Ganeti/HTools/Graph.hs
+++ b/htools/Ganeti/HTools/Graph.hs
@@ -138,10 +138,10 @@ isColorable g = isUndirected g && not (hasLoop g)
 verticesColors :: VertColorMap -> [Graph.Vertex] -> [Color]
 verticesColors cMap = mapMaybe (`IntMap.lookup` cMap)
 
--- | Get the colors of a list of vertices.
+-- | Get the set of colors of a list of vertices.
 -- Any uncolored vertices are ignored.
 verticesColorSet :: VertColorMap -> [Graph.Vertex] -> IntSet.IntSet
-verticesColorSet cMap = IntSet.fromList . mapMaybe (`IntMap.lookup` cMap)
+verticesColorSet cMap = IntSet.fromList . verticesColors cMap
 
 -- | Get the colors of the neighbors of a vertex.
 neighColors :: Graph.Graph -> VertColorMap -> Graph.Vertex -> [Color]