build | 2 +-

diff --git a/build b/build
index 0a2db2560a2d8e03b05f7cae039a55eca06f574995b097e318ed2ca53c2d8802..38a920461fca729a9e1c901234d69e78e2d2255e76b51fbe8d718f9d05abb1b1 100755
--- a/build
+++ b/build
@@ -1,7 +1,7 @@
 #!/bin/sh -e
 
 GO_FLAGS="${GO_FLAGS:--ldflags=-s}"
-GO_FLAGS="$GO_FLAGS -mod=vendor"
+[ ! -d vendor ] || GO_FLAGS="$GO_FLAGS -mod=vendor"
 ${GO:-go} build -o cmd/certgen/certgen $GO_FLAGS cmd/certgen/main.go
 ${GO:-go} build -o cmd/tofuproxy/tofuproxy $GO_FLAGS cmd/tofuproxy/main.go
 ${GO:-go} build -o cmd/warc-extract/warc-extract $GO_FLAGS cmd/warc-extract/main.go