diff --git a/metropolis/node/build/mkerofs/BUILD.bazel b/metropolis/node/build/mkerofs/BUILD.bazel
index 6de1c73..3cbcbde 100644
--- a/metropolis/node/build/mkerofs/BUILD.bazel
+++ b/metropolis/node/build/mkerofs/BUILD.bazel
@@ -6,7 +6,7 @@
     importpath = "source.monogon.dev/metropolis/node/build/mkerofs",
     visibility = ["//visibility:public"],
     deps = [
-        "//metropolis/node/build/mkerofs/fsspec:go_default_library",
+        "//metropolis/node/build/fsspec:go_default_library",
         "//metropolis/pkg/erofs:go_default_library",
         "@com_github_golang_protobuf//proto:go_default_library",
     ],
diff --git a/metropolis/node/build/mkerofs/fsspec/BUILD.bazel b/metropolis/node/build/mkerofs/fsspec/BUILD.bazel
deleted file mode 100644
index bd0f036..0000000
--- a/metropolis/node/build/mkerofs/fsspec/BUILD.bazel
+++ /dev/null
@@ -1,30 +0,0 @@
-load("@rules_proto//proto:defs.bzl", "proto_library")
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
-load("@io_bazel_rules_go//proto:def.bzl", "go_proto_library")
-
-proto_library(
-    name = "spec_proto",
-    srcs = ["spec.proto"],
-    visibility = ["//visibility:public"],
-)
-
-go_proto_library(
-    name = "spec_go_proto",
-    importpath = "source.monogon.dev/metropolis/node/build/mkerofs/spec",
-    proto = ":spec_proto",
-    visibility = ["//visibility:public"],
-)
-
-go_library(
-    name = "go_default_library",
-    embed = [":fsspec_go_proto"],
-    importpath = "source.monogon.dev/metropolis/node/build/mkerofs/fsspec",
-    visibility = ["//visibility:public"],
-)
-
-go_proto_library(
-    name = "fsspec_go_proto",
-    importpath = "source.monogon.dev/metropolis/node/build/mkerofs/fsspec",
-    proto = ":spec_proto",
-    visibility = ["//visibility:public"],
-)
diff --git a/metropolis/node/build/mkerofs/fsspec/spec.proto b/metropolis/node/build/mkerofs/fsspec/spec.proto
deleted file mode 100644
index 3d6e8dc..0000000
--- a/metropolis/node/build/mkerofs/fsspec/spec.proto
+++ /dev/null
@@ -1,70 +0,0 @@
-// Copyright 2020 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.
-
-syntax = "proto3";
-
-package metropolis.node.build.mkerofs.fsspec;
-option go_package = "source.monogon.dev/metropolis/node/build/mkerofs/fsspec";
-
-// FSSpec is the spec from which a filesystem is generated. It consists of files, directories and symbolic
-// links. Directories are also automatically inferred when required for the placement of files or symbolic
-// links. Inferred directories always have uid 0, gid 0 and permissions 0555. This can be overridden by
-// explicitly specifying a directory at a given path.
-message FSSpec {
-  repeated File file = 1;
-  repeated Directory directory = 2;
-  repeated SymbolicLink symbolic_link = 3;
-}
-
-// For internal use only. Represents all supported inodes in a oneof.
-message Inode {
-  oneof type {
-    File file = 1;
-    Directory directory = 2;
-    SymbolicLink symbolic_link = 3;
-  }
-}
-
-message File {
-  // The path where the file ends up in the filesystem.
-  string path = 1;
-  // The path on the host filesystem where the file contents should be taken from.
-  string source_path = 2;
-  // Unix permission bits
-  uint32 mode = 3;
-  // Owner uid
-  uint32 uid = 4;
-  // Owner gid
-  uint32 gid = 5;
-}
-
-message Directory {
-  // The path where the directory ends up in the filesystem.
-  string path = 1;
-  // Unix permission bits
-  uint32 mode = 2;
-  // Owner uid
-  uint32 uid = 3;
-  // Owner gid
-  uint32 gid = 4;
-}
-
-message SymbolicLink {
-  // The path where the symbolic link ends up in the filesystem.
-  string path = 1;
-  // The path to which the symbolic link resolves to.
-  string target_path = 2;
-}
\ No newline at end of file
diff --git a/metropolis/node/build/mkerofs/main.go b/metropolis/node/build/mkerofs/main.go
index d4e9d4d..651096b 100644
--- a/metropolis/node/build/mkerofs/main.go
+++ b/metropolis/node/build/mkerofs/main.go
@@ -30,7 +30,7 @@
 
 	"github.com/golang/protobuf/proto"
 
-	"source.monogon.dev/metropolis/node/build/mkerofs/fsspec"
+	"source.monogon.dev/metropolis/node/build/fsspec"
 	"source.monogon.dev/metropolis/pkg/erofs"
 )
 
@@ -161,6 +161,10 @@
 		entryRef.data.Type = &fsspec.Inode_SymbolicLink{SymbolicLink: symlink}
 	}
 
+	if len(spec.SpecialFile) > 0 {
+		log.Fatalf("special files are currently unimplemented in mkerofs")
+	}
+
 	fs, err := os.Create(*outPath)
 	if err != nil {
 		log.Fatalf("failed to open output file: %v", err)