diff --git a/CHANGELOG.md b/CHANGELOG.md
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,3 +1,7 @@
+# 0.3.4
+
+* Fix a regression in 0.3.3, which made `liftA2` too strict.
+
 # 0.3.3
 
 * Speed up `Applicative` / `Alternative` / `MonadPlus` instances.
diff --git a/Control/Monad/Omega.hs b/Control/Monad/Omega.hs
--- a/Control/Monad/Omega.hs
+++ b/Control/Monad/Omega.hs
@@ -1,4 +1,5 @@
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE LambdaCase #-}
 {-# OPTIONS_GHC -Wno-unrecognised-pragmas #-}
 {-# HLINT ignore "Avoid restricted function" #-}
 ----------------------------------------------
@@ -110,8 +111,12 @@
     pure = Omega . (:[])
     liftA2 f (Omega xs) = Omega . go [] . runOmega
         where
-            go initYs [] = concatMap (flip (zipWith f) initYs) (tails xs)
-            go initYs (y : ys) = zipWith f xs initYs  ++ go (y : initYs) ys
+            go [] = \case
+              [] -> []
+              y : ys -> go [y] ys
+            go initYs = (zipWith f xs initYs ++) . \case
+                [] -> concatMap (flip (zipWith f) initYs) (drop 1 (tails xs))
+                y : ys -> go (y : initYs) ys
 
 instance Applicative.Alternative Omega where
     empty = Omega []
diff --git a/control-monad-omega.cabal b/control-monad-omega.cabal
--- a/control-monad-omega.cabal
+++ b/control-monad-omega.cabal
@@ -1,6 +1,6 @@
 cabal-version:   2.0
 name:            control-monad-omega
-version:         0.3.3
+version:         0.3.4
 license:         PublicDomain
 maintainer:      lrpalmer@gmail.com
 author:          Luke Palmer
diff --git a/test/Properties.hs b/test/Properties.hs
--- a/test/Properties.hs
+++ b/test/Properties.hs
@@ -29,5 +29,36 @@
     let f x y = x * 10 + y in
     runOmega (liftA2 f (each xs) (each ys)) ===
       runOmega (join (each (map (\x -> each (map (\y -> f x y) ys)) xs)))
+
+  , testProperty "liftA2 (,) undefined []" $ once $
+    runOmega (liftA2 (,) undefined (each [])) === ([] :: [((), ())])
+  , testProperty "liftA2 (,) (1 : undefined) (1 : undefined)" $ once $
+    take 1 (runOmega (liftA2 (,) (each (1 : undefined)) (each (1 : undefined)))) === [(1, 1)]
+  , adjustOption (min (mkTimeout 1000000)) $
+    testProperty "enumerate arithGrammar" $ once $
+      take 10 (runOmega (enumerate arithGrammar)) ===
+        ["0","1","0+0","0*0","0+1","(0)","1+0","0*1","0+0*0","00"]
   ]
 
+-- From https://web.archive.org/web/20140823135714/http://lukepalmer.wordpress.com/2008/05/02/enumerating-a-context-free-language/
+
+data Symbol a
+  = Terminal a
+  | Nonterminal [[Symbol a]] -- a disjunction of juxtapositions
+
+enumerate :: Symbol a -> Omega [a]
+enumerate (Terminal a) = return [a]
+enumerate (Nonterminal alts) = do
+  alt <- each alts          -- for each alternative
+  rep <- mapM enumerate alt -- enumerate each symbol in the sequence
+  return $ concat rep       -- and concatenate the results
+
+arithGrammar :: Symbol Char
+arithGrammar = s
+  where
+    s      = Nonterminal [[add]]
+    add    = Nonterminal [[mul], [add, Terminal '+', mul]]
+    mul    = Nonterminal [[term], [mul, Terminal '*', term]]
+    term   = Nonterminal [[number], [Terminal '(', s, Terminal ')']]
+    digit  = Nonterminal $ map (map Terminal . show) [0..9]
+    number = Nonterminal [[digit], [digit, number]]