diff --git a/third_party/cap/external.bzl b/third_party/cap/external.bzl
new file mode 100644
index 0000000..075851b
--- /dev/null
+++ b/third_party/cap/external.bzl
@@ -0,0 +1,34 @@
+#  Copyright 2021 The Monogon Project Authors.
+#
+#  SPDX-License-Identifier: Apache-2.0
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+def cap_external(name, version):
+    sums = {
+        "1.2.55": "e29322032ea94e90696ae2d17530edc914c71765232ee8fd4fde38ba639cb256",
+    }
+
+    http_archive(
+        name = name,
+        sha256 = sums[version],
+        build_file = "@//third_party/cap:cap.bzl",
+        strip_prefix = "libcap-cap/v%s/libcap" % version,
+        patch_args = ["-p1"],
+        patches = [
+            "//third_party/cap/patches:add_go_codegen.patch",
+        ],
+        urls = ["https://git.kernel.org/pub/scm/libs/libcap/libcap.git/snapshot/libcap-cap/v%s.tar.gz" % version],
+    )