diff --git a/pkgs/applications/misc/pdfpc/default.nix b/pkgs/applications/misc/pdfpc/default.nix
index 1adab6b70a3e..a44cccf9a9d1 100644
--- a/pkgs/applications/misc/pdfpc/default.nix
+++ b/pkgs/applications/misc/pdfpc/default.nix
@@ -22,7 +22,7 @@ stdenv.mkDerivation rec {
   buildInputs = [ gstreamer gst-plugins-base gtk3 libgee poppler
     libpthreadstubs librsvg pcre ];
 
-  cmakeFlags = stdenv.lib.optionalString stdenv.isDarwin "-DMOVIES=OFF";
+  cmakeFlags = stdenv.lib.optional stdenv.isDarwin "-DMOVIES=OFF";
 
   patches = [
     # Fix build vala 0.46