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)