diff --git a/metropolis/node/build/mkerofs/fsspec/BUILD.bazel b/metropolis/node/build/fsspec/BUILD.bazel
similarity index 60%
rename from metropolis/node/build/mkerofs/fsspec/BUILD.bazel
rename to metropolis/node/build/fsspec/BUILD.bazel
index bd0f036..3a65d97 100644
--- a/metropolis/node/build/mkerofs/fsspec/BUILD.bazel
+++ b/metropolis/node/build/fsspec/BUILD.bazel
@@ -8,23 +8,16 @@
     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",
+    importpath = "source.monogon.dev/metropolis/node/build/fsspec",
     visibility = ["//visibility:public"],
 )
 
 go_proto_library(
     name = "fsspec_go_proto",
-    importpath = "source.monogon.dev/metropolis/node/build/mkerofs/fsspec",
+    importpath = "source.monogon.dev/metropolis/node/build/fsspec",
     proto = ":spec_proto",
     visibility = ["//visibility:public"],
 )
diff --git a/metropolis/node/build/mkerofs/fsspec/spec.proto b/metropolis/node/build/fsspec/spec.proto
similarity index 74%
rename from metropolis/node/build/mkerofs/fsspec/spec.proto
rename to metropolis/node/build/fsspec/spec.proto
index 3d6e8dc..712de1c 100644
--- a/metropolis/node/build/mkerofs/fsspec/spec.proto
+++ b/metropolis/node/build/fsspec/spec.proto
@@ -16,8 +16,8 @@
 
 syntax = "proto3";
 
-package metropolis.node.build.mkerofs.fsspec;
-option go_package = "source.monogon.dev/metropolis/node/build/mkerofs/fsspec";
+package metropolis.node.build.fsspec;
+option go_package = "source.monogon.dev/metropolis/node/build/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
@@ -27,6 +27,7 @@
   repeated File file = 1;
   repeated Directory directory = 2;
   repeated SymbolicLink symbolic_link = 3;
+  repeated SpecialFile special_file = 4;
 }
 
 // For internal use only. Represents all supported inodes in a oneof.
@@ -35,6 +36,7 @@
     File file = 1;
     Directory directory = 2;
     SymbolicLink symbolic_link = 3;
+    SpecialFile special_file = 4;
   }
 }
 
@@ -67,4 +69,30 @@
   string path = 1;
   // The path to which the symbolic link resolves to.
   string target_path = 2;
+}
+
+message SpecialFile {
+  // The path where the special file ends up in the filesystem.
+  string path = 1;
+
+  enum Type {
+    CHARACTER_DEV = 0;
+    BLOCK_DEV = 1;
+    FIFO = 2;
+  }
+
+  // Type of special file.
+  Type type = 2;
+
+  // The major device number of the special file.
+  uint32 major = 3;
+  // The minor number of the special file. Ignored for FIFO-type special files.
+  uint32 minor = 4;
+
+  // Unix permission bits
+  uint32 mode = 5;
+  // Owner uid
+  uint32 uid = 6;
+  // Owner gid
+  uint32 gid = 7;
 }
\ No newline at end of file
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/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)