diff --git a/pkgs/applications/networking/irc/communi/default.nix b/pkgs/applications/networking/irc/communi/default.nix
index 6cb6f2c2ef6..f3a840e23d0 100644
--- a/pkgs/applications/networking/irc/communi/default.nix
+++ b/pkgs/applications/networking/irc/communi/default.nix
@@ -19,16 +19,17 @@ stdenv.mkDerivation rec {
 
   preConfigure = ''
     export QMAKEFEATURES=${libcommuni}/features
-    qmakeFlags="$qmakeFlags \
-      COMMUNI_INSTALL_PREFIX=$out \
-      COMMUNI_INSTALL_BINS=$out/bin \
-      COMMUNI_INSTALL_PLUGINS=$out/lib/communi/plugins \
-      COMMUNI_INSTALL_ICONS=$out/share/icons/hicolor \
-      COMMUNI_INSTALL_DESKTOP=$out/share/applications \
-      COMMUNI_INSTALL_THEMES=$out/share/communi/themes
-    "
   '';
 
+  qmakeFlags = [
+    "COMMUNI_INSTALL_PREFIX=${placeholder "out"}"
+    "COMMUNI_INSTALL_BINS=${placeholder "out"}/bin"
+    "COMMUNI_INSTALL_PLUGINS=${placeholder "out"}/lib/communi/plugins"
+    "COMMUNI_INSTALL_ICONS=${placeholder "out"}/share/icons/hicolor"
+    "COMMUNI_INSTALL_DESKTOP=${placeholder "out"}/share/applications"
+    "COMMUNI_INSTALL_THEMES=${placeholder "out"}/share/communi/themes"
+  ];
+
   postInstall = stdenv.lib.optionalString stdenv.isLinux ''
     substituteInPlace "$out/share/applications/communi.desktop" \
       --replace "/usr/bin" "$out/bin"