diff --git a/pomaps.cabal b/pomaps.cabal
--- a/pomaps.cabal
+++ b/pomaps.cabal
@@ -1,5 +1,5 @@
 name:           pomaps
-version:        0.2.0.0
+version:        0.2.0.1
 synopsis:       Maps and sets of partial orders
 category:       Data Structures
 homepage:       https://github.com/sgraf812/pomaps#readme
@@ -10,7 +10,7 @@
 license-file:   LICENSE.md
 build-type:     Simple
 cabal-version:  >= 1.10
-tested-with:    GHC ==8.8.1 || ==8.6.5 || ==8.4.4 || ==8.2.2
+tested-with:    GHC ==9.0.1 || ==8.10.2 || ==8.8.4 || ==8.6.5 || ==8.4.4 || ==8.2.2
 
 extra-source-files:
     CHANGELOG.md
@@ -34,15 +34,15 @@
       src
   ghc-options: -Wall
   build-depends:
-      base >= 4.6.0.0 && < 4.14
+      base >= 4.6.0.0 && < 4.15
     -- oneShot
-    , ghc-prim >= 0.4 && < 0.6
+    , ghc-prim >= 0.4 && < 0.7
     , deepseq >= 1.1 && < 1.5
     -- We depend on the internal modules of containers,
     -- so we have to track development really close.
     -- Data.Map.Internal is only available since 0.5.9,
     -- of which 0.5.9.2 is the first safe version
-    , containers >= 0.5.9.2 && <= 0.6.2.1
+    , containers >= 0.5.9.2 && <= 0.6.4.1
     -- We need PartialOrd instances for ()
     , lattices >= 1.7
   exposed-modules:
diff --git a/src/Data/POMap/Internal.hs b/src/Data/POMap/Internal.hs
--- a/src/Data/POMap/Internal.hs
+++ b/src/Data/POMap/Internal.hs
@@ -577,7 +577,7 @@
       case (k `leq` k', k' `leq` k) of
         (True, True) -> Found $ case f k (Just v') of
           Just v  -> seq' s v (Bin n k' v l r)
-          Nothing -> Tip
+          Nothing -> Map.link2 l r
         (True, False)  -> oneShot (\l' -> Map.balanceL k' v' l' r) <$> go l
         (False, True)  -> oneShot (\r' -> Map.balanceR k' v' l r') <$> go r
         (False, False) -> Incomparable
@@ -615,7 +615,7 @@
       case (k `leq` k', k' `leq` k) of
         (True, True) -> Found (Just v', case f k (Just v') of
           Just v  -> seq' s v (Bin n k' v l r)
-          Nothing -> Tip)
+          Nothing -> Map.link2 l r)
         (True, False)  -> second (oneShot (\l' -> Map.balanceL k' v' l' r)) <$> go l
         (False, True)  -> second (oneShot (\r' -> Map.balanceR k' v' l r')) <$> go r
         (False, False) -> Incomparable
@@ -672,7 +672,7 @@
         (True, True)   ->
           ret Found (Just v) . oneShot $ \case
             Just v' -> seq' s v' (Bin n k v' l r)
-            Nothing -> Tip
+            Nothing -> Map.link2 l r
         (True, False)  -> lift (go l) . oneShot $ \l' -> Map.balanceL k' v l' r
         (False, True)  -> lift (go r) . oneShot $ \r' -> Map.balanceL k' v l r'
         (False, False) -> Incomparable
diff --git a/tests/Data/POMap/Properties.hs b/tests/Data/POMap/Properties.hs
--- a/tests/Data/POMap/Properties.hs
+++ b/tests/Data/POMap/Properties.hs
@@ -1,7 +1,7 @@
 {-# LANGUAGE FlexibleInstances   #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections #-}
-{-# OPTIONS_GHC -fno-warn-orphans #-}
+{-# OPTIONS_GHC -O0 -fno-warn-orphans #-}
 module Data.POMap.Properties where
 
 import           Algebra.PartialOrd
@@ -21,6 +21,7 @@
 import           Data.POMap.Arbitrary    ()
 import           Data.POMap.Divisibility
 import           Data.POMap.Lazy
+import qualified Data.POSet              as POSet
 import           Data.Traversable
 import           Prelude                 hiding (filter, lookup, map, max, null)
 import           Test.Tasty.Hspec
@@ -58,6 +59,11 @@
 isAntichain []     = True
 isAntichain (x:xs) = all (not . comparable x) xs && isAntichain xs
 
+newtype OrdInt = OrdInt Int deriving (Eq, Show)
+instance PartialOrd OrdInt where OrdInt sa `leq` OrdInt sb = sa <= sb
+instance Arbitrary OrdInt where
+  arbitrary = OrdInt <$> arbitrary
+
 spec :: Spec
 spec =
   describe "POMap" $ do
@@ -549,3 +555,20 @@
           fmap (+1) m `shouldBe` fmapDefault (+1) m
         it "foldMap = foldMapDefault" $ property $ \(m :: DivMap Int) ->
           foldMap Sum m `shouldBe` foldMapDefault Sum m
+
+    describe "regression tests" $ do
+      describe "#3" $ do
+        it "example 1" $ do
+          let e = OrdInt 13
+          let s1 = POSet.delete e $
+                   POSet.fromList [ OrdInt 0, OrdInt 32, e ]
+          let s2 = POSet.fromList [ OrdInt 0, OrdInt 32 ]
+          s1 `shouldBe` s2
+          length s1 `shouldBe` 2
+        it "example 2" $ do
+          let e = OrdInt 0
+          let s1 = POSet.delete e $
+                   POSet.fromList [ e, OrdInt 1 ]
+          let s2 = POSet.fromList [ OrdInt 1 ]
+          s1 `shouldBe` s2
+          length s1 `shouldBe` 1