diff --git a/pkgs/development/libraries/qt-4.x/4.8/default.nix b/pkgs/development/libraries/qt-4.x/4.8/default.nix
index 05b2c582cc2..8b3fd8c6678 100644
--- a/pkgs/development/libraries/qt-4.x/4.8/default.nix
+++ b/pkgs/development/libraries/qt-4.x/4.8/default.nix
@@ -183,7 +183,7 @@ stdenv.mkDerivation rec {
       [ "-I${glib.dev}/include/glib-2.0" "-I${glib.out}/lib/glib-2.0/include" ]
     ++ optional stdenv.isDarwin "-I${libcxx}/include/c++/v1";
 
-  NIX_LDFLAGS = optional (stdenv.isFreeBSD || stdenv.isDarwin) "-lglib-2.0";
+  NIX_LDFLAGS = optionalString (stdenv.isFreeBSD || stdenv.isDarwin) "-lglib-2.0";
 
   preBuild = optionalString stdenv.isDarwin ''
     # resolve "extra qualification on member" error