diff --git a/pkgs/development/libraries/git2/default.nix b/pkgs/development/libraries/git2/default.nix
index 3c4c2703d6f..abb782641dd 100644
--- a/pkgs/development/libraries/git2/default.nix
+++ b/pkgs/development/libraries/git2/default.nix
@@ -10,6 +10,8 @@ stdenv.mkDerivation rec {
     sha256 = "1iyncz8fqazw683dxjls3lf5pw3f5ma8kachkvjz7dsq57wxllbj";
   };
 
+  cmakeFlags = "-DTHREADSAFE=ON";
+
   nativeBuildInputs = [ cmake python ];
   buildInputs = [ zlib ];