diff --git a/go.mod b/go.mod
new file mode 100644
index 0000000..88c746a
--- /dev/null
+++ b/go.mod
@@ -0,0 +1,9 @@
+module github.com/mmcloughlin/avo
+
+require (
+	github.com/campoy/embedmd v1.0.0 // indirect
+	github.com/dlespiau/covertool v0.0.0-20180314162135-b0c4c6d0583a // indirect
+	github.com/urfave/cli v1.20.0 // indirect
+	golang.org/x/arch v0.0.0-20181203225421-5a4828bb7045
+	golang.org/x/tools v0.0.0-20190106171756-3ef68632349c
+)
diff --git a/go.sum b/go.sum
new file mode 100644
index 0000000..b355117
--- /dev/null
+++ b/go.sum
@@ -0,0 +1,12 @@
+github.com/campoy/embedmd v1.0.0 h1:V4kI2qTJJLf4J29RzI/MAt2c3Bl4dQSYPuflzwFH2hY=
+github.com/campoy/embedmd v1.0.0/go.mod h1:oxyr9RCiSXg0M3VJ3ks0UGfp98BpSSGr0kpiX3MzVl8=
+github.com/dlespiau/covertool v0.0.0-20180314162135-b0c4c6d0583a h1:+cYgqwB++gEE09SluRYGqJyDhWmLmdWZ2cXlOXSGV8w=
+github.com/dlespiau/covertool v0.0.0-20180314162135-b0c4c6d0583a/go.mod h1:/eQMcW3eA1bzKx23ZYI2H3tXPdJB5JWYTHzoUPBvQY4=
+github.com/pmezard/go-difflib v1.0.0 h1:4DBwDE0NGyQoBHbLQYPwSUPoCMWR5BEzIk/f1lZbAQM=
+github.com/pmezard/go-difflib v1.0.0/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/urfave/cli v1.20.0 h1:fDqGv3UG/4jbVl/QkFwEdddtEDjh/5Ov6X+0B/3bPaw=
+github.com/urfave/cli v1.20.0/go.mod h1:70zkFmudgCuE/ngEzBv17Jvp/497gISqfk5gWijbERA=
+golang.org/x/arch v0.0.0-20181203225421-5a4828bb7045 h1:Pn8fQdvx+z1avAi7fdM2kRYWQNxGlavNDSyzrQg2SsU=
+golang.org/x/arch v0.0.0-20181203225421-5a4828bb7045/go.mod h1:cYlCBUl1MsqxdiKgmc4uh7TxZfWSFLOGSRR090WDxt8=
+golang.org/x/tools v0.0.0-20190106171756-3ef68632349c h1:mYpOyPbwiBWL7unJZKj7TctJ0vXSRdNUQBq8pGosFgI=
+golang.org/x/tools v0.0.0-20190106171756-3ef68632349c/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
diff --git a/script/bootstrap b/script/bootstrap
index 78b4a25..dd48814 100755
--- a/script/bootstrap
+++ b/script/bootstrap
@@ -1,9 +1,7 @@
 #!/bin/bash -ex
 
-# Limit dependencies to golang.org/x repos
-go get -u \
-    golang.org/x/arch/x86/... \
-    golang.org/x/tools/go/...
+# Install go module dependencies.
+go mod download
 
 # Install golangci-lint
 golangci_lint_version='v1.12.3'