diff --git a/hcl2template/mock.go b/hcl2template/mock.go
index 09fbf0c19..8576a0439 100644
--- a/hcl2template/mock.go
+++ b/hcl2template/mock.go
@@ -40,8 +40,8 @@ var _ packer.Builder = new(MockBuilder)
 
 func (b *MockBuilder) ConfigSpec() hcldec.ObjectSpec { return b.Config.FlatMapstructure().HCL2Spec() }
 
-func (b *MockBuilder) Prepare(raws ...interface{}) ([]string, error) {
-	return nil, config.Decode(&b.Config, &config.DecodeOpts{
+func (b *MockBuilder) Prepare(raws ...interface{}) ([]string, []string, error) {
+	return nil, nil, config.Decode(&b.Config, &config.DecodeOpts{
 		Interpolate: true,
 	}, raws...)
 }
@@ -70,7 +70,7 @@ func (b *MockProvisioner) Prepare(raws ...interface{}) error {
 	}, raws...)
 }
 
-func (b *MockProvisioner) Provision(ctx context.Context, ui packer.Ui, comm packer.Communicator) error {
+func (b *MockProvisioner) Provision(ctx context.Context, ui packer.Ui, comm packer.Communicator, _ map[string]interface{}) error {
 	return nil
 }
 
diff --git a/hcl2template/types.source.go b/hcl2template/types.source.go
index f86ab4b69..7b1216e2a 100644
--- a/hcl2template/types.source.go
+++ b/hcl2template/types.source.go
@@ -61,7 +61,8 @@ func (p *Parser) StartBuilder(source *Source) (packer.Builder, hcl.Diagnostics)
 	if moreDiags.HasErrors() {
 		return nil, diags
 	}
-	warning, err := builder.Prepare(decoded)
+
+	_, warning, err := builder.Prepare(decoded)
 	moreDiags = warningErrorsToDiags(source.block, warning, err)
 	diags = append(diags, moreDiags...)
 	return builder, diags