diff --git a/lib/vagrant/machine_index.rb b/lib/vagrant/machine_index.rb
index 64a26666b..42ea7328a 100644
--- a/lib/vagrant/machine_index.rb
+++ b/lib/vagrant/machine_index.rb
@@ -171,27 +171,40 @@ module Vagrant
       id     = entry.id
 
       @lock.synchronize do
-        # Verify the machine is locked so we can safely write
-        # to it.
-        if !id
-          id = SecureRandom.uuid.gsub("-", "")
-          lock_file = lock_machine(id)
-          if !lock_file
-            raise "Failed to lock new machine: #{entry.name}"
+        with_index_lock do
+          # Reload so we have the latest machine data. This allows other
+          # processes to update their own machines without conflicting
+          # with our own.
+          unlocked_reload
+
+          # If we don't have a machine ID, try to look one up
+          if !id
+            self.each do |other|
+              if entry.name == other.name &&
+                entry.provider == other.provider &&
+                entry.vagrantfile_path.to_s == other.vagrantfile_path.to_s
+                id = other.id
+                break
+              end
+            end
+
+            # If we still don't have an ID, generate a random one
+            id = SecureRandom.uuid.gsub("-", "") if !id
+
+            # Get a lock on this machine
+            lock_file = lock_machine(id)
+            if !lock_file
+              raise "Failed to lock new machine: #{entry.name}"
+            end
+
+            @machine_locks[id] = lock_file
           end
 
-          @machine_locks[id] = lock_file
-        end
+          if !@machine_locks[id]
+            raise "Unlocked write on machine: #{id}"
+          end
 
-        if !@machine_locks[id]
-          raise "Unlocked write on machine: #{id}"
-        end
-
-        with_index_lock do
-          # Reload so we have the latest machine data, then update
-          # this particular machine, then write. This allows other processes
-          # to update their own machines without conflicting with our own.
-          unlocked_reload
+          # Set our machine and save
           @machines[id] = struct
           unlocked_save
         end
@@ -218,6 +231,8 @@ module Vagrant
     #
     # If the lock cannot be acquired, then nil is returned.
     #
+    # This should be called within an index lock.
+    #
     # @return [File]
     def lock_machine(uuid)
       lock_path = @data_dir.join("#{uuid}.lock")
diff --git a/test/unit/vagrant/machine_index_test.rb b/test/unit/vagrant/machine_index_test.rb
index 58eed8896..69a753052 100644
--- a/test/unit/vagrant/machine_index_test.rb
+++ b/test/unit/vagrant/machine_index_test.rb
@@ -227,5 +227,39 @@ describe Vagrant::MachineIndex do
         "foo" => "bar",
       })
     end
+
+    it "updates an existing directory if the name, provider, and path are the same" do
+      entry = entry_klass.new
+      entry.name = "foo"
+      entry.provider = "bar"
+      entry.vagrantfile_path = "/bar"
+      entry.state = "foo"
+
+      result = subject.set(entry)
+      expect(result.id).to_not be_empty
+
+      # Release it so we can modify it
+      subject.release(result)
+
+      entry2 = entry_klass.new
+      entry2.name = entry.name
+      entry2.provider = entry.provider
+      entry2.vagrantfile_path = entry.vagrantfile_path
+      entry2.state = "bar"
+      expect(entry2.id).to be_nil
+
+      nextresult = subject.set(entry2)
+      expect(nextresult.id).to eq(result.id)
+
+      # Release it so we can test the contents
+      subject.release(nextresult)
+
+      # Get it from a new class and check the results
+      subject = described_class.new(data_dir)
+      entry   = subject.get(result.id)
+      expect(entry).to_not be_nil
+      expect(entry.name).to eq(entry2.name)
+      expect(entry.state).to eq(entry2.state)
+    end
   end
 end