diff --git a/Makefile b/Makefile
index 0b6e407925..a4d11fa2c5 100644
--- a/Makefile
+++ b/Makefile
@@ -4,9 +4,8 @@
 
 VERSION := 0.15.0-dev
 
-# Always use the vendor directory. Remove this
-# when the OPA vendor directory is removed.
-GO := GOFLAGS=-mod=vendor go
+# Force modules on and to use the vendor directory.
+GO := GO111MODULE=on GOFLAGS=-mod=vendor go
 GOVERSION := 1.12.9
 GOARCH := $(shell go env GOARCH)
 GOOS := $(shell go env GOOS)