diff --git a/plugins/kernel_v2/config/disk.rb b/plugins/kernel_v2/config/disk.rb
index e1480be24..95b8005f3 100644
--- a/plugins/kernel_v2/config/disk.rb
+++ b/plugins/kernel_v2/config/disk.rb
@@ -169,12 +169,13 @@ module VagrantPlugins
           if @size.is_a?(String)
             @size = Vagrant::Util::Numeric.string_to_bytes(@size)
           end
-
-          if !@size
-            errors << I18n.t("vagrant.config.disk.invalid_size", name: @name, machine: machine.name)
-          end
         end
 
+        if !@size
+          errors << I18n.t("vagrant.config.disk.invalid_size", name: @name, machine: machine.name)
+        end
+
+
         if @file
           if !@file.is_a?(String)
             errors << I18n.t("vagrant.config.disk.invalid_file_type", file: @file, machine: machine.name)
diff --git a/test/unit/plugins/kernel_v2/config/disk_test.rb b/test/unit/plugins/kernel_v2/config/disk_test.rb
index 0d7a39959..cb37ead49 100644
--- a/test/unit/plugins/kernel_v2/config/disk_test.rb
+++ b/test/unit/plugins/kernel_v2/config/disk_test.rb
@@ -56,6 +56,16 @@ describe VagrantPlugins::Kernel_V2::VagrantConfigDisk do
     end
   end
 
+  describe "with an invalid config" do
+    let(:invalid_subject) { described_class.new(type) }
+
+    it "raises an error if size not set" do
+      invalid_subject.name = "bar"
+      subject.finalize!
+      assert_invalid
+    end
+  end
+
   describe "defining a new config that needs to match internal restraints" do
     before do
     end