diff --git a/Data/SortedList.hs b/Data/SortedList.hs
--- a/Data/SortedList.hs
+++ b/Data/SortedList.hs
@@ -217,10 +217,11 @@
 {-# INLINE delete #-}
 delete a (SortedList l) = SortedList $ go l
   where
-    go (x:xs)
-      | x < a = x : go xs
-      | x > a = x : xs
-      | otherwise = xs
+    go (x:xs) =
+      case x `compare` a of
+        LT -> x : go xs
+        GT -> x : xs
+        EQ -> xs
     go [] = []
 
 -- | Extract the prefix with the given length from a sorted list.
diff --git a/LICENSE b/LICENSE
--- a/LICENSE
+++ b/LICENSE
@@ -1,4 +1,4 @@
-Copyright (c) 2015, Daniel Díaz
+Copyright (c) 2023, Daniel Casanueva
 
 All rights reserved.
 
@@ -13,7 +13,7 @@
       disclaimer in the documentation and/or other materials provided
       with the distribution.
 
-    * Neither the name of Daniel Díaz nor the names of other
+    * Neither the name of Daniel Casanueva nor the names of other
       contributors may be used to endorse or promote products derived
       from this software without specific prior written permission.
 
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,2 +1,6 @@
+## 0.2.1.2
+* Use `compare` instead of inequalities in `delete` implementation.
+* Add test.
+
 ## 0.2.1.1
 * Improve `delete` implementation.
diff --git a/sorted-list.cabal b/sorted-list.cabal
--- a/sorted-list.cabal
+++ b/sorted-list.cabal
@@ -1,5 +1,5 @@
 name:                sorted-list
-version:             0.2.1.1
+version:             0.2.1.2
 synopsis:            Type-enforced sorted lists and related functions.
 description:         Type-enforced sorted lists and related functions.
                      .
@@ -35,18 +35,27 @@
 extra-doc-files:     readme.md, changelog.md
 
 library
-  exposed-modules:     Data.SortedList
-  build-depends:       base == 4.*
-               ,       deepseq
   default-language:    Haskell2010
   ghc-options:         -Wall
+  build-depends:       base == 4.*
+               ,       deepseq
+  exposed-modules:     Data.SortedList
 
 benchmark sorted-list-map-bench
   default-language: Haskell2010
   type: exitcode-stdio-1.0
   hs-source-dirs: bench
   main-is: map.hs
+  ghc-options: -O2 -Wall
   build-depends: base == 4.*
                , sorted-list
                , criterion
-  ghc-options: -O2 -Wall
+
+test-suite sorted-list-tests
+  default-language: Haskell2010
+  type: exitcode-stdio-1.0
+  hs-source-dirs: tests
+  main-is: Main.hs
+  ghc-options: -Wall
+  default-extensions: ImportQualifiedPost
+  build-depends: base, sorted-list, QuickCheck
diff --git a/tests/Main.hs b/tests/Main.hs
new file mode 100644
--- /dev/null
+++ b/tests/Main.hs
@@ -0,0 +1,42 @@
+
+{-# OPTIONS_GHC -Wno-orphans #-}
+
+module Main (main) where
+
+import Control.Monad (unless)
+import Test.QuickCheck
+  ( Testable, isSuccess, quickCheckResult
+  , Arbitrary, arbitrary
+    )
+import System.Exit (exitFailure)
+import Data.SortedList (SortedList)
+import Data.SortedList qualified as SL
+import Data.List qualified as List
+
+-- | Test a property.
+quickCheck :: Testable prop => String -> prop -> IO ()
+quickCheck n p = do
+  putStrLn $ "Testing property: " ++ n
+  r <- quickCheckResult p
+  unless (isSuccess r) exitFailure
+
+instance (Arbitrary a, Ord a) => Arbitrary (SortedList a) where
+  arbitrary = SL.toSortedList <$> arbitrary
+
+applyAsList :: Ord a => ([a] -> [a]) -> SortedList a -> SortedList a
+applyAsList f = SL.toSortedList . f . SL.fromSortedList
+
+main :: IO ()
+main = do
+  quickCheck "toSortedList . fromSortedList = id" $
+    \xs -> applyAsList id xs == (xs :: SortedList Int)
+  quickCheck "insert" $
+    \x xs -> SL.insert x xs == applyAsList ((:) x) (xs :: SortedList Int)
+  quickCheck "delete" $
+    \x xs -> let ys :: SortedList Int
+                 ys = SL.toSortedList $ x : xs
+             in  SL.delete x ys == applyAsList (List.delete x) ys
+  quickCheck "elemOrd" $
+    \x xs -> SL.elemOrd x xs == List.elem (x :: Int) (SL.fromSortedList xs)
+  quickCheck "nub" $
+    \xs -> SL.nub xs == applyAsList List.nub (xs :: SortedList Int)