diff --git a/go/packages/golist_overlay.go b/go/packages/golist_overlay.go
index b35399ef..ffc7a367 100644
--- a/go/packages/golist_overlay.go
+++ b/go/packages/golist_overlay.go
@@ -32,6 +32,13 @@ func processGolistOverlay(cfg *Config, response *responseDeduper) (modifiedPkgs,
 	var rootDirs map[string]string
 	var onceGetRootDirs sync.Once
 
+	// If no new imports are added, it is safe to avoid loading any needPkgs.
+	// Otherwise, it's hard to tell which package is actually being loaded
+	// (due to vendoring) and whether any modified package will show up
+	// in the transitive set of dependencies (because new imports are added,
+	// potentially modifying the transitive set of dependencies).
+	var overlayAddsImports bool
+
 	for opath, contents := range cfg.Overlay {
 		base := filepath.Base(opath)
 		dir := filepath.Dir(opath)
@@ -136,6 +143,7 @@ func processGolistOverlay(cfg *Config, response *responseDeduper) (modifiedPkgs,
 		for _, imp := range imports {
 			_, found := pkg.Imports[imp]
 			if !found {
+				overlayAddsImports = true
 				// TODO(matloob): Handle cases when the following block isn't correct.
 				// These include imports of test variants, imports of vendored packages, etc.
 				id, ok := havePkgs[imp]
@@ -171,9 +179,11 @@ func processGolistOverlay(cfg *Config, response *responseDeduper) (modifiedPkgs,
 		}
 	}
 
-	needPkgs = make([]string, 0, len(needPkgsSet))
-	for pkg := range needPkgsSet {
-		needPkgs = append(needPkgs, pkg)
+	if overlayAddsImports {
+		needPkgs = make([]string, 0, len(needPkgsSet))
+		for pkg := range needPkgsSet {
+			needPkgs = append(needPkgs, pkg)
+		}
 	}
 	modifiedPkgs = make([]string, 0, len(modifiedPkgsSet))
 	for pkg := range modifiedPkgsSet {