diff --git a/gopls/internal/lsp/cache/snapshot.go b/gopls/internal/lsp/cache/snapshot.go
index 52c5a26fc7b..ac92e8cd79d 100644
--- a/gopls/internal/lsp/cache/snapshot.go
+++ b/gopls/internal/lsp/cache/snapshot.go
@@ -1440,50 +1440,30 @@ func (s *snapshot) GetCriticalError(ctx context.Context) *source.CriticalError {
 	return loadErr
 }
 
+// A portion of this text is expected by TestBrokenWorkspace_OutsideModule.
 const adHocPackagesWarning = `You are outside of a module and outside of $GOPATH/src.
 If you are using modules, please open your editor to a directory in your module.
 If you believe this warning is incorrect, please file an issue: https://github.com/golang/go/issues/new.`
 
 func shouldShowAdHocPackagesWarning(snapshot source.Snapshot, pkgs []source.Package) string {
-	if snapshot.ValidBuildConfiguration() {
-		return ""
-	}
-	for _, pkg := range pkgs {
-		if hasMissingDependencies(pkg) {
-			return adHocPackagesWarning
-		}
-	}
-	return ""
-}
+	if !snapshot.ValidBuildConfiguration() {
+		for _, pkg := range pkgs {
+			// TODO(adonovan): strength-reduce the parameter to []Metadata.
+			m := snapshot.Metadata(pkg.ID())
+			if m == nil {
+				continue
+			}
 
-func hasMissingDependencies(pkg source.Package) bool {
-	// We don't invalidate metadata for import deletions,
-	// so check the package imports via the syntax tree
-	// (not via types.Package.Imports, since it contains packages
-	// synthesized under the vendoring-hostile assumption that
-	// ImportPath equals PackagePath).
-	//
-	// rfindley says: it looks like this is intending to implement
-	// a heuristic "if go list couldn't resolve import paths to
-	// packages, then probably you're not in GOPATH or a module".
-	// This is used to determine if we need to show a warning diagnostic.
-	// It looks like this logic is implementing the heuristic that
-	// "even if the metadata has a MissingDep, if the types.Package
-	// doesn't need that dep anymore we shouldn't show the warning".
-	// But either we're outside of GOPATH/Module, or we're not...
-	//
-	// If we invalidate the metadata for import deletions (which
-	// should be fast) then we can simply return the blank entries
-	// in DepsByImpPath.
-	for _, f := range pkg.GetSyntax() {
-		for _, imp := range f.Imports {
-			importPath := source.UnquoteImportPath(imp)
-			if _, err := pkg.ResolveImportPath(importPath); err != nil {
-				return true
+			// A blank entry in DepsByImpPath
+			// indicates a missing dependency.
+			for _, importID := range m.DepsByImpPath {
+				if importID == "" {
+					return adHocPackagesWarning
+				}
 			}
 		}
 	}
-	return false
+	return ""
 }
 
 func containsCommandLineArguments(pkgs []source.Package) bool {
diff --git a/gopls/internal/regtest/diagnostics/diagnostics_test.go b/gopls/internal/regtest/diagnostics/diagnostics_test.go
index fb858f6ab5d..880b62f7654 100644
--- a/gopls/internal/regtest/diagnostics/diagnostics_test.go
+++ b/gopls/internal/regtest/diagnostics/diagnostics_test.go
@@ -543,6 +543,10 @@ func _() {
 // Expect a module/GOPATH error if there is an error in the file at startup.
 // Tests golang/go#37279.
 func TestBrokenWorkspace_OutsideModule(t *testing.T) {
+	// Versions of the go command before go1.16 do not support
+	// native overlays and so do not observe the deletion.
+	testenv.NeedsGo1Point(t, 16)
+
 	const noModule = `
 -- a.go --
 package foo
@@ -556,8 +560,10 @@ func f() {
 	Run(t, noModule, func(t *testing.T, env *Env) {
 		env.OpenFile("a.go")
 		env.Await(
+			// Expect the adHocPackagesWarning.
 			OutstandingWork(lsp.WorkspaceLoadFailure, "outside of a module"),
 		)
+		// Deleting the import dismisses the warning.
 		env.RegexpReplace("a.go", `import "mod.com/hello"`, "")
 		env.Await(
 			NoOutstandingWork(),