diff --git a/pkgs/by-name/op/openldap/package.nix b/pkgs/by-name/op/openldap/package.nix
index 3ebf541856ef..cf67b943b3c9 100644
--- a/pkgs/by-name/op/openldap/package.nix
+++ b/pkgs/by-name/op/openldap/package.nix
@@ -108,14 +108,14 @@ stdenv.mkDerivation rec {
   ];
 
   postBuild = ''
-    for module in $extraContribModules; do
-      make $makeFlags CC=$CC -C contrib/slapd-modules/$module
+    for module in ''${extraContribModules[@]}; do
+      make ''${makeFlags[@]} CC=$CC -C contrib/slapd-modules/$module
     done
   '';
 
   preCheck = ''
     substituteInPlace tests/scripts/all \
-      --replace "/bin/rm" "rm"
+      --replace-fail "/bin/rm" "rm"
 
     # skip flaky tests
     # https://bugs.openldap.org/show_bug.cgi?id=8623
@@ -144,8 +144,8 @@ stdenv.mkDerivation rec {
   ];
 
   postInstall = lib.optionalString withModules ''
-    for module in $extraContribModules; do
-      make $installFlags install -C contrib/slapd-modules/$module
+    for module in ''${extraContribModules[@]}; do
+      make ''${installFlags[@]} install -C contrib/slapd-modules/$module
     done
     chmod +x "$out"/lib/*.{so,dylib}
   '';