diff --git a/pkgs/development/libraries/fancypp/default.nix b/pkgs/development/libraries/fancypp/default.nix
index a4fe5cc70af2..f93ab77c63de 100644
--- a/pkgs/development/libraries/fancypp/default.nix
+++ b/pkgs/development/libraries/fancypp/default.nix
@@ -5,7 +5,7 @@
 
 stdenvNoCC.mkDerivation rec {
   pname = "fancypp";
-  version = "2021-04-08";
+  version = "unstable-2021-04-08";
 
   src = fetchFromGitHub {
     owner = "Curve";