diff --git a/plugins/kernel_v2/config/disk.rb b/plugins/kernel_v2/config/disk.rb
index e443f5f8a..90ca1c781 100644
--- a/plugins/kernel_v2/config/disk.rb
+++ b/plugins/kernel_v2/config/disk.rb
@@ -11,7 +11,6 @@ module VagrantPlugins
       #-------------------------------------------------------------------
 
       DEFAULT_DISK_TYPES = [:disk, :dvd, :floppy].freeze
-      DEFAULT_DISK_EXT = ["vdi", "vmdk", "vhd", "vhdx"].freeze
 
       # Note: This value is for internal use only
       #
@@ -136,13 +135,18 @@ module VagrantPlugins
                            types: DEFAULT_DISK_TYPES.join(', '))
         end
 
-        if !DEFAULT_DISK_EXT.include?(@disk_ext)
-          errors << I18n.t("vagrant.config.disk.invalid_ext", ext: @disk_ext,
-                           name: @name, exts: DEFAULT_DISK_EXT.join(', ') )
-        end
-
         if @disk_ext
           @disk_ext = @disk_ext.downcase
+
+          if machine.provider.capability?(:validate_disk_ext)
+            if !machine.provider.capability(:validate_disk_ext, @disk_ext)
+              errors << I18n.t("vagrant.config.disk.invalid_ext", ext: @disk_ext,
+                               name: @name,
+                               exts: machine.provider.capability(:get_default_disk_ext).join(', '))
+            end
+          else
+            @logger.warn("No provider capability defined to validate 'disk_ext' type")
+          end
         end
 
         if @size && !@size.is_a?(Integer)
diff --git a/plugins/providers/virtualbox/cap/validate_disk_ext.rb b/plugins/providers/virtualbox/cap/validate_disk_ext.rb
new file mode 100644
index 000000000..3715a91d0
--- /dev/null
+++ b/plugins/providers/virtualbox/cap/validate_disk_ext.rb
@@ -0,0 +1,27 @@
+require "log4r"
+
+module VagrantPlugins
+  module ProviderVirtualBox
+    module Cap
+      module ValidateDiskExt
+        LOGGER = Log4r::Logger.new("vagrant::plugins::virtualbox::validate_disk_ext")
+
+        # The default set of disk formats that VirtualBox supports
+        DEFAULT_DISK_EXT = ["vdi", "vmdk", "vhd"].freeze
+
+        # @param [Vagrant::Machine] machine
+        # @param [String] disk_ext
+        # @return [Bool]
+        def self.validate_disk_ext(machine, disk_ext)
+          DEFAULT_DISK_EXT.include?(disk_ext)
+        end
+
+        # @param [Vagrant::Machine] machine
+        # @return [Array]
+        def self.get_default_disk_ext(machine)
+          DEFAULT_DISK_EXT
+        end
+      end
+    end
+  end
+end
diff --git a/plugins/providers/virtualbox/plugin.rb b/plugins/providers/virtualbox/plugin.rb
index e5b3e03a5..9cb46b54e 100644
--- a/plugins/providers/virtualbox/plugin.rb
+++ b/plugins/providers/virtualbox/plugin.rb
@@ -49,6 +49,16 @@ module VagrantPlugins
         Cap::CleanupDisks
       end
 
+      provider_capability(:virtualbox, :validate_disk_ext) do
+        require_relative "cap/validate_disk_ext"
+        Cap::ValidateDiskExt
+      end
+
+      provider_capability(:virtualbox, :get_default_disk_ext) do
+        require_relative "cap/validate_disk_ext"
+        Cap::ValidateDiskExt
+      end
+
       provider_capability(:virtualbox, :snapshot_list) do
         require_relative "cap"
         Cap