diff --git a/hcl2template/types.build.go b/hcl2template/types.build.go
index a90ad67b6..30705c55b 100644
--- a/hcl2template/types.build.go
+++ b/hcl2template/types.build.go
@@ -57,7 +57,7 @@ func (p *Parser) decodeBuildConfig(block *hcl.Block) (*BuildBlock, hcl.Diagnosti
 	build := &BuildBlock{}
 
 	var b struct {
-		FromSources []string `hcl:"sources"`
+		FromSources []string `hcl:"sources,optional"`
 		Config      hcl.Body `hcl:",remain"`
 	}
 	diags := gohcl.DecodeBody(block.Body, nil, &b)