diff --git a/builder/builder.go b/builder/builder.go
index dd8d366..3d1e49b 100644
--- a/builder/builder.go
+++ b/builder/builder.go
@@ -51,6 +51,10 @@ var UseNewSwupdServer = false
 // building the chroots. This is an experimental feature.
 var UseNewChrootBuilder = false
 
+// Offline controls whether mixer attempts to automatically cache upstream
+// bundles. In offline mode, all necessary bundles must exist in local-bundles.
+var Offline = false
+
 // A Builder contains all configurable fields required to perform a full mix
 // operation, and is used to encapsulate life time data.
 type Builder struct {
@@ -498,6 +502,10 @@ func getUpstreamBundlesPath(ver string) string {
 }
 
 func (b *Builder) getUpstreamBundles(ver string, prune bool) error {
+	if Offline {
+		return nil
+	}
+
 	// Make the folder to store upstream bundles if does not exist
 	if err := os.MkdirAll(upstreamBundlesBaseDir, 0777); err != nil {
 		return errors.Wrap(err, "Failed to create upstream-bundles dir.")
@@ -946,7 +954,10 @@ func (b *Builder) ListBundles(listType listType, tree bool) error {
 	}
 	upstreamBundles, err := b.getDirBundlesListAsSet(getUpstreamBundlesPath(b.UpstreamVer))
 	if err != nil {
-		return err
+		if !Offline {
+			return err
+		}
+		upstreamBundles = make(bundleSet)
 	}
 
 	// Assign "top level" bundles
diff --git a/mixer/cmd/root.go b/mixer/cmd/root.go
index b451526..a98f0e8 100644
--- a/mixer/cmd/root.go
+++ b/mixer/cmd/root.go
@@ -146,6 +146,8 @@ func init() {
 	// TODO: Remove this once we migrate to new implementation.
 	RootCmd.PersistentFlags().BoolVar(&builder.UseNewSwupdServer, "new-swupd", false, "EXPERIMENTAL: Use new implementation of swupd-server when possible")
 
+	RootCmd.PersistentFlags().BoolVar(&builder.Offline, "offline", false, "Skip caching upstream-bundles; work entirely with local-bundles")
+
 	RootCmd.AddCommand(initCmd)
 	RootCmd.Flags().BoolVar(&rootCmdFlags.version, "version", false, "Print version information and quit")
 	RootCmd.Flags().BoolVar(&rootCmdFlags.check, "check", false, "Check all dependencies needed by mixer and quit")