diff --git a/Math/Combinatorics/Multiset.hs b/Math/Combinatorics/Multiset.hs
--- a/Math/Combinatorics/Multiset.hs
+++ b/Math/Combinatorics/Multiset.hs
@@ -11,6 +11,7 @@
 
          Count
        , Multiset(..)
+       , emptyMS, singletonMS
        , consMS, (+:)
 
          -- ** Conversions
@@ -82,11 +83,21 @@
 liftMS :: ([(a, Count)] -> [(b, Count)]) -> Multiset a -> Multiset b
 liftMS f (MS m) = MS (f m)
 
+-- | A multiset with no values in it.
+emptyMS :: Multiset a
+emptyMS = MS []
+
+-- | Create a multiset with only a single value in it.
+singletonMS :: a -> Multiset a
+singletonMS a = MS [(a,1)]
+
 -- | Add an element with multiplicity to a multiset.  Precondition:
 --   the new element is distinct from all elements already in the
 --   multiset.
 consMS :: (a, Count) -> Multiset a -> Multiset a
-consMS e (MS m) = MS (e:m)
+consMS e@(_,c) (MS m)
+  | c > 0     = MS (e:m)
+  | otherwise = MS m
 
 -- | A convenient shorthand for 'consMS'.
 (+:) :: (a, Count) -> Multiset a -> Multiset a
diff --git a/multiset-comb.cabal b/multiset-comb.cabal
--- a/multiset-comb.cabal
+++ b/multiset-comb.cabal
@@ -1,5 +1,5 @@
 Name:                multiset-comb
-Version:             0.2.1
+Version:             0.2.2
 Synopsis:            Combinatorial algorithms over multisets
 Description:         Various combinatorial algorithms over multisets,
                      including generating all permutations,
@@ -13,7 +13,7 @@
 Copyright:           (c) 2010 Brent Yorgey
 Stability:           Experimental
 Category:            Math
-Tested-with:         GHC ==6.10.4, GHC ==6.12.1
+Tested-with:         GHC ==6.10.4, GHC ==6.12.1, GHC ==7.0.3
 Build-type:          Simple
 Cabal-version:       >=1.6
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