diff --git a/src/cmd/go/internal/modindex/read.go b/src/cmd/go/internal/modindex/read.go
index 83d5faf28f..bda3fb4338 100644
--- a/src/cmd/go/internal/modindex/read.go
+++ b/src/cmd/go/internal/modindex/read.go
@@ -124,7 +124,7 @@ var (
 	errNotFromModuleCache = fmt.Errorf("%w: not from module cache", ErrNotIndexed)
 )
 
-// GetPackage returns the IndexPackage for the package at the given path.
+// GetPackage returns the IndexPackage for the directory at the given path.
 // It will return ErrNotIndexed if the directory should be read without
 // using the index, for instance because the index is disabled, or the package
 // is not in a module.
@@ -669,11 +669,9 @@ func IsStandardPackage(goroot_, compiler, path string) bool {
 		reldir = str.TrimFilePathPrefix(reldir, "cmd")
 		modroot = filepath.Join(modroot, "cmd")
 	}
-	if _, err := GetPackage(modroot, filepath.Join(modroot, reldir)); err == nil {
-		// Note that goroot.IsStandardPackage doesn't check that the directory
-		// actually contains any go files-- merely that it exists. GetPackage
-		// returning a nil error is enough for us to know the directory exists.
-		return true
+	if pkg, err := GetPackage(modroot, filepath.Join(modroot, reldir)); err == nil {
+		hasGo, err := pkg.IsDirWithGoFiles()
+		return err == nil && hasGo
 	} else if errors.Is(err, ErrNotIndexed) {
 		// Fall back because package isn't indexable. (Probably because
 		// a file was modified recently)
@@ -786,8 +784,8 @@ func shouldBuild(sf *sourceFile, tags map[string]bool) bool {
 	return true
 }
 
-// IndexPackage holds the information needed to access information in the
-// index needed to load a package in a specific directory.
+// IndexPackage holds the information in the index
+// needed to load a package in a specific directory.
 type IndexPackage struct {
 	error error
 	dir   string // directory of the package relative to the modroot
diff --git a/src/cmd/go/testdata/script/list_testdata.txt b/src/cmd/go/testdata/script/list_testdata.txt
new file mode 100644
index 0000000000..d62dd55c7d
--- /dev/null
+++ b/src/cmd/go/testdata/script/list_testdata.txt
@@ -0,0 +1,11 @@
+# Issue 65406. The testdata directory in GOROOT/src
+# shouldn't be treated as a standard package.
+
+go list -f '{{.ImportPath}} {{.Dir}}' testdata
+! stderr 'found package testdata in multiple modules'
+stdout 'testdata '$WORK${/}'gopath'${/}'src'
+
+-- go.mod --
+module testdata
+-- p.go --
+package p
\ No newline at end of file
diff --git a/src/cmd/go/testdata/script/mod_list.txt b/src/cmd/go/testdata/script/mod_list.txt
index 06316cc335..40820b3bb5 100644
--- a/src/cmd/go/testdata/script/mod_list.txt
+++ b/src/cmd/go/testdata/script/mod_list.txt
@@ -44,9 +44,9 @@ stderr '^go: module rsc.io/quote/buggy: not a known dependency'
 
 # Module loader does not interfere with list -e (golang.org/issue/24149).
 go list -e -f '{{.Error.Err}}' database
-stdout 'no Go files in '
+stdout 'package database is not in std'
 ! go list database
-stderr 'no Go files in '
+stderr 'package database is not in std'
 
 -- go.mod --
 module x
diff --git a/src/internal/goroot/gc.go b/src/internal/goroot/gc.go
index c0216f4ea5..6b37dfa4c7 100644
--- a/src/internal/goroot/gc.go
+++ b/src/internal/goroot/gc.go
@@ -20,8 +20,16 @@ func IsStandardPackage(goroot, compiler, path string) bool {
 	switch compiler {
 	case "gc":
 		dir := filepath.Join(goroot, "src", path)
-		info, err := os.Stat(dir)
-		return err == nil && info.IsDir()
+		dirents, err := os.ReadDir(dir)
+		if err != nil {
+			return false
+		}
+		for _, dirent := range dirents {
+			if strings.HasSuffix(dirent.Name(), ".go") {
+				return true
+			}
+		}
+		return false
 	case "gccgo":
 		return gccgoSearch.isStandard(path)
 	default:
diff --git a/src/internal/goroot/gccgo.go b/src/internal/goroot/gccgo.go
index 62841222a7..2bbf4cda2b 100644
--- a/src/internal/goroot/gccgo.go
+++ b/src/internal/goroot/gccgo.go
@@ -9,6 +9,7 @@ package goroot
 import (
 	"os"
 	"path/filepath"
+	"strings"
 )
 
 // IsStandardPackage reports whether path is a standard package,
@@ -17,8 +18,16 @@ func IsStandardPackage(goroot, compiler, path string) bool {
 	switch compiler {
 	case "gc":
 		dir := filepath.Join(goroot, "src", path)
-		_, err := os.Stat(dir)
-		return err == nil
+		dirents, err := os.ReadDir(dir)
+		if err != nil {
+			return false
+		}
+		for _, dirent := range dirents {
+			if strings.HasSuffix(dirent.Name(), ".go") {
+				return true
+			}
+		}
+		return false
 	case "gccgo":
 		return stdpkg[path]
 	default: