diff --git a/pkgs/development/python-modules/pycapnp/default.nix b/pkgs/development/python-modules/pycapnp/default.nix
index cd2e8f450cd2..fc41822cebe3 100644
--- a/pkgs/development/python-modules/pycapnp/default.nix
+++ b/pkgs/development/python-modules/pycapnp/default.nix
@@ -33,5 +33,8 @@ buildPythonPackage rec {
     homepage = "https://capnproto.github.io/pycapnp/";
     maintainers = with maintainers; [ cstrahan lukeadams ];
     license = licenses.bsd2;
+    # No support for capnproto 1.0 yet
+    # https://github.com/capnproto/pycapnp/issues/323
+    broken = lib.versionAtLeast capnproto.version "1.0";
   };
 }