diff --git a/Cabal/src/Distribution/Simple/GHC/Build.hs b/Cabal/src/Distribution/Simple/GHC/Build.hs
index 75e40de07b5..4f50309ad39 100644
--- a/Cabal/src/Distribution/Simple/GHC/Build.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Build.hs
@@ -17,6 +17,7 @@ import Distribution.Simple.Program
 import Distribution.Simple.Utils
 import Distribution.Types.ComponentLocalBuildInfo (componentIsIndefinite)
 import Distribution.Types.ParStrat
+import Distribution.Utils.NubList (fromNubListR)
 import System.Directory hiding (exeExtension)
 import System.FilePath
 
@@ -136,4 +137,4 @@ build numJobs pkg_descr pbci = do
   -- generated from compiling Haskell modules (#842, #3294).
   buildOpts <- buildHaskellModules numJobs ghcProg pkg_descr buildTargetDir_absolute wantedWays pbci
   extraSources <- buildAllExtraSources ghcProg buildTargetDir pbci
-  linkOrLoadComponent ghcProg pkg_descr extraSources (buildTargetDir, targetDir_absolute) (wantedWays, buildOpts) pbci
+  linkOrLoadComponent ghcProg pkg_descr (fromNubListR extraSources) (buildTargetDir, targetDir_absolute) (wantedWays, buildOpts) pbci
diff --git a/Cabal/src/Distribution/Simple/GHC/Build/ExtraSources.hs b/Cabal/src/Distribution/Simple/GHC/Build/ExtraSources.hs
index 37e45a49f7c..12dac910b75 100644
--- a/Cabal/src/Distribution/Simple/GHC/Build/ExtraSources.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Build/ExtraSources.hs
@@ -10,6 +10,7 @@ import Distribution.Simple.Flag
 import qualified Distribution.Simple.GHC.Internal as Internal
 import Distribution.Simple.Program.GHC
 import Distribution.Simple.Utils
+import Distribution.Utils.NubList
 
 import Distribution.Types.BuildInfo
 import Distribution.Types.Component
@@ -34,15 +35,16 @@ buildAllExtraSources
   -- ^ The build directory for this target
   -> PreBuildComponentInputs
   -- ^ The context and component being built in it.
-  -> IO [FilePath]
-  -- ^ Returns the list of extra sources that were built
-buildAllExtraSources = mconcat
-  [ buildCSources
-  , buildCxxSources
-  , buildJsSources
-  , buildAsmSources
-  , buildCmmSources
-  ]
+  -> IO (NubListR FilePath)
+  -- ^ Returns the (nubbed) list of extra sources that were built
+buildAllExtraSources =
+  mconcat
+    [ buildCSources
+    , buildCxxSources
+    , buildJsSources
+    , buildAsmSources
+    , buildCmmSources
+    ]
 
 buildCSources
   , buildCxxSources
@@ -55,7 +57,7 @@ buildCSources
     -- ^ The build directory for this target
     -> PreBuildComponentInputs
     -- ^ The context and component being built in it.
-    -> IO [FilePath]
+    -> IO (NubListR FilePath)
     -- ^ Returns the list of extra sources that were built
 buildCSources =
   buildExtraSources
@@ -137,7 +139,7 @@ buildExtraSources
   -- ^ The build directory for this target
   -> PreBuildComponentInputs
   -- ^ The context and component being built in it.
-  -> IO [FilePath]
+  -> IO (NubListR FilePath)
   -- ^ Returns the list of extra sources that were built
 buildExtraSources description componentSourceGhcOptions wantDyn viewSources ghcProg buildTargetDir =
   \PreBuildComponentInputs{buildingWhat, localBuildInfo = lbi, targetInfo} ->
@@ -233,8 +235,8 @@ buildExtraSources description componentSourceGhcOptions wantDyn viewSources ghcP
      in
       -- build any sources
       if (null sources || componentIsIndefinite clbi)
-        then return []
+        then return mempty
         else do
           info verbosity ("Building " ++ description ++ "...")
           traverse_ buildAction sources
-          return sources
+          return (toNubListR sources)
diff --git a/Cabal/src/Distribution/Simple/GHC/Build/Link.hs b/Cabal/src/Distribution/Simple/GHC/Build/Link.hs
index 1cd174c0a0f..04295340b82 100644
--- a/Cabal/src/Distribution/Simple/GHC/Build/Link.hs
+++ b/Cabal/src/Distribution/Simple/GHC/Build/Link.hs
@@ -182,7 +182,7 @@ linkLibrary
   :: FilePath
   -- ^ The library target build directory
   -> [FilePath]
-  -- ^ The list of extra lib dirs that exist (aka cleaned)
+  -- ^ The list of extra lib dirs that exist (aka "cleaned")
   -> PackageDescription
   -- ^ The package description containing this library
   -> Verbosity