diff --git a/helper/resource/map.go b/helper/resource/map.go
index 301db8b144..523c24b8e4 100644
--- a/helper/resource/map.go
+++ b/helper/resource/map.go
@@ -44,8 +44,7 @@ func (m *Map) Apply(
 	if s.ID == "" {
 		return r.Create(s, d, meta)
 	} else {
-		panic("update no implemented yet")
-		//return r.Update(s, d, meta)
+		return r.Update(s, d, meta)
 	}
 }
 
diff --git a/helper/resource/map_test.go b/helper/resource/map_test.go
new file mode 100644
index 0000000000..958e3540f7
--- /dev/null
+++ b/helper/resource/map_test.go
@@ -0,0 +1 @@
+package resource
diff --git a/helper/resource/resource.go b/helper/resource/resource.go
index 3409228d10..0437b34e1f 100644
--- a/helper/resource/resource.go
+++ b/helper/resource/resource.go
@@ -9,6 +9,7 @@ type Resource struct {
 	Destroy DestroyFunc
 	Diff    DiffFunc
 	Refresh RefreshFunc
+	Update  UpdateFunc
 }
 
 // CreateFunc is a function that creates a resource that didn't previously
@@ -35,3 +36,12 @@ type DiffFunc func(
 type RefreshFunc func(
 	*terraform.ResourceState,
 	interface{}) (*terraform.ResourceState, error)
+
+// UpdateFunc is a function that is called to update a resource that
+// previously existed. The difference between this and CreateFunc is that
+// the diff is guaranteed to only contain attributes that don't require
+// a new resource.
+type UpdateFunc func(
+	*terraform.ResourceState,
+	*terraform.ResourceDiff,
+	interface{}) (*terraform.ResourceState, error)