diff --git a/CHANGELOG.md b/CHANGELOG.md
index d0d93c0a8e6..065faa34c41 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ BUG FIXES:
   - providers/docker: Protocol is now honored in direct `ports settings.
   - providers/docker: Images built using `build\_dir` will more robustly
       capture the final image. [GH-4598]
+  - providers/docker: NFS synced folders now work. [GH-4344]
   - providers/virtualbox: Show a human-friendly error if VirtualBox didn't
       clean up an existing VM. [GH-4681]
   - provisioners/docker: Search for docker binary in multiple places. [GH-4580]
diff --git a/plugins/providers/virtualbox/action.rb b/plugins/providers/virtualbox/action.rb
index 668cbe0efea..83eb3aec96c 100644
--- a/plugins/providers/virtualbox/action.rb
+++ b/plugins/providers/virtualbox/action.rb
@@ -292,6 +292,16 @@ def self.action_suspend
         end
       end
 
+      # This is the action that is called to sync folders to a running
+      # machine without a reboot.
+      def self.action_sync_folders
+        Vagrant::Action::Builder.new.tap do |b|
+          b.use PrepareNFSValidIds
+          b.use SyncedFolders
+          b.use PrepareNFSSettings
+        end
+      end
+
       # This action brings the machine up from nothing, including importing
       # the box, configuring metadata, and booting.
       def self.action_up
diff --git a/plugins/providers/virtualbox/action/prepare_nfs_settings.rb b/plugins/providers/virtualbox/action/prepare_nfs_settings.rb
index b88cee99f59..b7a92d1acab 100644
--- a/plugins/providers/virtualbox/action/prepare_nfs_settings.rb
+++ b/plugins/providers/virtualbox/action/prepare_nfs_settings.rb
@@ -1,7 +1,10 @@
+require "vagrant/action/builtin/mixin_synced_folders"
+
 module VagrantPlugins
   module ProviderVirtualBox
     module Action
       class PrepareNFSSettings
+        include Vagrant::Action::Builtin::MixinSyncedFolders
         include Vagrant::Util::Retryable
 
         def initialize(app, env)
@@ -14,7 +17,13 @@ def call(env)
 
           @app.call(env)
 
-          if using_nfs?
+          opts = {
+            cached: !!env[:synced_folders_cached],
+            config: env[:synced_folders_config],
+          }
+          folders = synced_folders(env[:machine], **opts)
+
+          if folders.has_key?(:nfs)
             @logger.info("Using NFS, preparing NFS settings by reading host IP and machine IP")
             add_ips_to_env!(env)
           end