diff --git a/Data/SortedList.hs b/Data/SortedList.hs
--- a/Data/SortedList.hs
+++ b/Data/SortedList.hs
@@ -92,6 +92,10 @@
 #if MIN_VERSION_base(4,9,0)
 import Data.Semigroup (Semigroup (..))
 #endif
+--
+#if !MIN_VERSION_base(4,18,0)
+import Control.Applicative (liftA2)
+#endif
 
 -- | Type of sorted lists. Any (non-bottom) value of this type
 --   is a sorted list. Use the 'Monoid' instance to merge sorted
@@ -367,7 +371,7 @@
   #-}
 
 -- | Traverse a sorted list with a function that returns in a monad.
---   The same performance observations apply here than in 'map', as
+--   The same performance observations apply here as in 'map', as
 --   changing the values may involve reordering the list.
 --
 --   @since 0.2.3.0
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,3 +1,6 @@
+## 0.2.3.1
+* Extend support below base-4.18.
+
 ## 0.2.3.0
 * Update metadata.
 * Add `traverse`.
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:             0.2.3.0
+version:             0.2.3.1
 synopsis:            Type-enforced sorted lists and related functions.
 description:         Type-enforced sorted lists and related functions.
                      .