diff --git a/pkgs/tools/filesystems/irods/common.nix b/pkgs/tools/filesystems/irods/common.nix
index 33edc0e4a05b..c2e09220a957 100644
--- a/pkgs/tools/filesystems/irods/common.nix
+++ b/pkgs/tools/filesystems/irods/common.nix
@@ -27,15 +27,13 @@
     "-DCPACK_GENERATOR=TGZ"
     "-DCMAKE_CXX_FLAGS=-I${lib.getDev libcxx}/include/c++/v1"
     "-DPAM_LIBRARY=${pam}/lib/libpam.so"
+    "-DCMAKE_INSTALL_PREFIX=${placeholder "out"}"
+    "-DIRODS_HOME_DIRECTORY=${placeholder "out"}"
+    "-DCMAKE_INSTALL_SBINDIR=${placeholder "out"}/sbin"
   ];
 
   postPatch = ''
     patchShebangs ./packaging ./scripts
-    export cmakeFlags="$cmakeFlags
-      -DCMAKE_INSTALL_PREFIX=$out
-      -DIRODS_HOME_DIRECTORY=$out
-      -DCMAKE_INSTALL_SBINDIR=$out/sbin
-    "
   '';
 
   meta = with lib; {
diff --git a/pkgs/tools/filesystems/irods/default.nix b/pkgs/tools/filesystems/irods/default.nix
index 5db0ed453eab..beddb6959ba4 100644
--- a/pkgs/tools/filesystems/irods/default.nix
+++ b/pkgs/tools/filesystems/irods/default.nix
@@ -32,6 +32,12 @@ rec {
     # fix build with recent llvm versions
     env.NIX_CFLAGS_COMPILE = "-Wno-deprecated-register -Wno-deprecated-declarations";
 
+    cmakeFlags = common.cmakeFlags or [ ] ++ [
+      "-DCMAKE_EXE_LINKER_FLAGS=-Wl,-rpath,${placeholder "out"}/lib"
+      "-DCMAKE_MODULE_LINKER_FLAGS=-Wl,-rpath,${placeholder "out"}/lib"
+      "-DCMAKE_SHARED_LINKER_FLAGS=-Wl,-rpath,${placeholder "out"}/lib"
+    ];
+
     postPatch = common.postPatch + ''
       patchShebangs ./test
       substituteInPlace plugins/database/CMakeLists.txt --replace-fail "COMMAND cpp" "COMMAND ${gcc.cc}/bin/cpp"
@@ -39,11 +45,6 @@ rec {
       do
         substituteInPlace $file --replace-quiet "CATCH2}/include" "CATCH2}/include/catch2"
       done
-      export cmakeFlags="$cmakeFlags
-        -DCMAKE_EXE_LINKER_FLAGS=-Wl,-rpath,$out/lib
-        -DCMAKE_MODULE_LINKER_FLAGS=-Wl,-rpath,$out/lib
-        -DCMAKE_SHARED_LINKER_FLAGS=-Wl,-rpath,$out/lib
-        "
 
       substituteInPlace server/auth/CMakeLists.txt --replace-fail SETUID ""
     '';