diff --git a/website/source/docs/extending/custom-builders.html.md b/website/source/docs/extending/custom-builders.html.md
index 63cfdb40b..1cd2b6094 100644
--- a/website/source/docs/extending/custom-builders.html.md
+++ b/website/source/docs/extending/custom-builders.html.md
@@ -31,7 +31,8 @@ method should do.
 
 ``` go
 type Builder interface {
-  Prepare(...interface{}) error
+  ConfigSpec() hcldec.ObjectSpec
+  Prepare(...interface{}) ([]string, []string, error)
   Run(context.Context, ui Ui, hook Hook) (Artifact, error)
 }
 ```
diff --git a/website/source/docs/extending/custom-post-processors.html.md b/website/source/docs/extending/custom-post-processors.html.md
index e940047b3..7f717346a 100644
--- a/website/source/docs/extending/custom-post-processors.html.md
+++ b/website/source/docs/extending/custom-post-processors.html.md
@@ -36,6 +36,7 @@ explaining what each method should do.
 
 ``` go
 type PostProcessor interface {
+  ConfigSpec() hcldec.ObjectSpec
   Configure(interface{}) error
   PostProcess(context.Context, Ui, Artifact) (a Artifact, keep, mustKeep bool, err error)
 }
diff --git a/website/source/docs/extending/custom-provisioners.html.md b/website/source/docs/extending/custom-provisioners.html.md
index 7cfd55939..0d6d7f15b 100644
--- a/website/source/docs/extending/custom-provisioners.html.md
+++ b/website/source/docs/extending/custom-provisioners.html.md
@@ -35,8 +35,9 @@ explaining what each method should do.
 
 ``` go
 type Provisioner interface {
+  ConfigSpec() hcldec.ObjectSpec
   Prepare(...interface{}) error
-  Provision(Ctx, Ui, Communicator, new(interface{})) error
+  Provision(context.Context, Ui, Communicator, map[string]interface{}) error
 }
 ```