diff --git a/pkgs/development/libraries/cpp-gsl/default.nix b/pkgs/development/libraries/cpp-gsl/default.nix
index ecd86354ee8..833275c72bd 100644
--- a/pkgs/development/libraries/cpp-gsl/default.nix
+++ b/pkgs/development/libraries/cpp-gsl/default.nix
@@ -12,6 +12,7 @@ stdenv.mkDerivation rec {
     sha256 = "0h8py468bvxnydkjs352d7a9s8hk0ihc7msjkcnzj2d7nzp5nsc1";
   };
 
+  NIX_CFLAGS_COMPILE = "-Wno-error=sign-conversion";
   nativeBuildInputs = [ cmake catch ];
 
   meta = with stdenv.lib; {