diff --git a/pkgs/development/haskell-modules/with-packages-wrapper.nix b/pkgs/development/haskell-modules/with-packages-wrapper.nix
index 081190188742..32fa46fd04ac 100644
--- a/pkgs/development/haskell-modules/with-packages-wrapper.nix
+++ b/pkgs/development/haskell-modules/with-packages-wrapper.nix
@@ -113,7 +113,7 @@ symlinkJoin {
     # Clean up the old links that may have been (transitively) included by
     # symlinkJoin:
     rm -f $dynamicLinksDir/*
-    for d in $(grep dynamic-library-dirs $packageConfDir/*|awk '{print $2}'|sort -u); do
+    for d in $(grep -Poz "dynamic-library-dirs:\s*\K .+\n" $packageConfDir/*|awk '{print $2}'|sort -u); do
       ln -s $d/*.dylib $dynamicLinksDir
     done
     for f in $packageConfDir/*.conf; do
@@ -123,7 +123,7 @@ symlinkJoin {
       # $dynamicLinksDir
       cp $f $f-tmp
       rm $f
-      sed "s,dynamic-library-dirs: .*,dynamic-library-dirs: $dynamicLinksDir," $f-tmp > $f
+      sed "N;s,dynamic-library-dirs:\s*.*,dynamic-library-dirs: $dynamicLinksDir," $f-tmp > $f
       rm $f-tmp
     done
   '') + ''