diff --git a/pkgs/development/libraries/capnproto/default.nix b/pkgs/development/libraries/capnproto/default.nix
index 7493426e227f..713a49dbaa6c 100644
--- a/pkgs/development/libraries/capnproto/default.nix
+++ b/pkgs/development/libraries/capnproto/default.nix
@@ -1,4 +1,4 @@
-{ lib, stdenv, fetchurl, cmake }:
+{ lib, stdenv, fetchurl, capnproto, cmake }:
 
 stdenv.mkDerivation rec {
   pname = "capnproto";
@@ -9,7 +9,10 @@ stdenv.mkDerivation rec {
     sha256 = "sha256-soBUp6K/6kK/w5LI0AljDZTXLozoaiOtbxi15yV0Bk8=";
   };
 
-  nativeBuildInputs = [ cmake ];
+  nativeBuildInputs = [ cmake ]
+    ++ lib.optional (!(stdenv.hostPlatform.isCompatible stdenv.buildPlatform)) capnproto;
+
+  cmakeFlags = lib.optional (!(stdenv.hostPlatform.isCompatible stdenv.buildPlatform)) "-DEXTERNAL_CAPNP";
 
   meta = with lib; {
     homepage    = "https://capnproto.org/";