diff --git a/hcl2template/parser.go b/hcl2template/parser.go
index 1c3430dea..82372bac1 100644
--- a/hcl2template/parser.go
+++ b/hcl2template/parser.go
@@ -474,8 +474,13 @@ func (cfg *PackerConfig) evaluateBuildPrereqs(skipDatasources bool) hcl.Diagnost
 
 func (cfg *PackerConfig) Initialize(opts packer.InitializeOptions) hcl.Diagnostics {
 	diags := cfg.InputVariables.ValidateValues()
-	diags = append(diags, cfg.evaluateDatasources(opts.SkipDatasourcesExecution)...)
-	diags = append(diags, cfg.evaluateLocalVariables(cfg.LocalBlocks)...)
+
+	if opts.UseSequential {
+		diags = diags.Extend(cfg.evaluateDatasources(opts.SkipDatasourcesExecution))
+		diags = diags.Extend(cfg.evaluateLocalVariables(cfg.LocalBlocks))
+	} else {
+		diags = diags.Extend(cfg.evaluateBuildPrereqs(opts.SkipDatasourcesExecution))
+	}
 
 	filterVarsFromLogs(cfg.InputVariables)
 	filterVarsFromLogs(cfg.LocalVariables)
diff --git a/packer/run_interfaces.go b/packer/run_interfaces.go
index 07829e629..3b7170899 100644
--- a/packer/run_interfaces.go
+++ b/packer/run_interfaces.go
@@ -38,6 +38,14 @@ type InitializeOptions struct {
 	// When set, the execution of datasources will be skipped and the datasource will provide
 	// an output spec that will be used for validation only.
 	SkipDatasourcesExecution bool
+	// UseSequential changes the way data sources and locals are evaluated.
+	//
+	// In this mode, instead of using two separate phases to evaluate datasources first, then
+	// local variables, here we instead use a DAG so both are evaluated at once, based on the
+	// dependencies between them.
+	//
+	// This is optional and defaults to false for now, but this may become a default later.
+	UseSequential bool
 }
 
 type PluginBinaryDetector interface {