diff --git a/src/Data/MultiKeyedMap.hs b/src/Data/MultiKeyedMap.hs
--- a/src/Data/MultiKeyedMap.hs
+++ b/src/Data/MultiKeyedMap.hs
@@ -23,7 +23,6 @@
 , mkMKMap, fromList, toList
 , insert
 , flattenKeys, keys, values
-, mapKeys
 ) where
 
 import qualified Data.Map.Strict as M
@@ -150,15 +149,7 @@
     ins = newVal [k] v m
     upd ik = MKMap { keyMap, highestIk, valMap = M.insert ik v valMap }
 
--- | Map function over all keys. See 'M.mapKeys'.
---
--- TODO: Might leak space if a k is mapped to an
--- already existing k', because k’s value might not be
--- referenced anymore.
-mapKeys :: (Ord k') => (k -> k') -> MKMap k v -> MKMap k' v
-mapKeys f MKMap{..} = MKMap { keyMap = M.mapKeys f keyMap, .. }
 
-
 -- | Helper, assumes there is no such value already.
 -- Will leak space otherwise!
 --
@@ -172,4 +163,3 @@
         , highestIk = next
         , valMap = M.insert next v valMap }
   where next = succ highestIk
-
diff --git a/yarn-lock.cabal b/yarn-lock.cabal
--- a/yarn-lock.cabal
+++ b/yarn-lock.cabal
@@ -3,7 +3,7 @@
 -- see: https://github.com/sol/hpack
 
 name:           yarn-lock
-version:        0.3.2
+version:        0.3.3
 synopsis:       Represent and parse yarn.lock files
 description:    Types and parser for the lock file format of the npm successor yarn. All modules should be imported qualified.
 category:       Data
@@ -31,7 +31,7 @@
       base >= 4.9 && < 4.10
     , containers
     , text
-    , megaparsec == 5.* || == 6.*
+    , megaparsec == 5.*
     , protolude >= 0.1
     , either == 4.*
   exposed-modules:
@@ -55,7 +55,7 @@
       base >= 4.9 && < 4.10
     , containers
     , text
-    , megaparsec == 5.* || == 6.*
+    , megaparsec == 5.*
     , protolude >= 0.1
     , either == 4.*
     , yarn-lock