diff --git a/pkgs/applications/video/mythtv/default.nix b/pkgs/applications/video/mythtv/default.nix
index 52bfb76529f9..c4b40178b32d 100644
--- a/pkgs/applications/video/mythtv/default.nix
+++ b/pkgs/applications/video/mythtv/default.nix
@@ -25,4 +25,8 @@ stdenv.mkDerivation {
     ./settings.patch
     ./purity.patch # don't search in /usr/include etc.
   ];
+
+  /* Quick workaround for NIXPKGS-30 to get floor() etc. to work in
+     MythTV.  Can be removed once NIXPKGS-30 has been fixed. */
+  NIX_CFLAGS_COMPILE = "-ffast-math";
 }