diff --git a/pkgs/development/libraries/qt-5/default.nix b/pkgs/development/libraries/qt-5/default.nix
index 3f75e6aeb9b2..98fd20c44c00 100644
--- a/pkgs/development/libraries/qt-5/default.nix
+++ b/pkgs/development/libraries/qt-5/default.nix
@@ -160,6 +160,9 @@ stdenv.mkDerivation rec {
 
   nativeBuildInputs = [ python perl pkgconfig ];
 
+  # freetype-2.5.4 changed signedness of some struct fields
+  NIX_CFLAGS_COMPILE = "-Wno-error=sign-compare";
+
   postInstall =
     ''
       ${optionalString buildDocs ''