diff --git a/src/cmd/addr2line/addr2line_test.go b/src/cmd/addr2line/addr2line_test.go
index 183a22f8f3..22bf1379bb 100644
--- a/src/cmd/addr2line/addr2line_test.go
+++ b/src/cmd/addr2line/addr2line_test.go
@@ -115,5 +115,3 @@ func TestAddr2Line(t *testing.T) {
 	testAddr2Line(t, exepath, syms[symName])
 	testAddr2Line(t, exepath, "0x"+syms[symName])
 }
-
-func init() { testenv.SetModVendor() }
diff --git a/src/cmd/compile/internal/gc/scope_test.go b/src/cmd/compile/internal/gc/scope_test.go
index e4861c686c..e327dc02af 100644
--- a/src/cmd/compile/internal/gc/scope_test.go
+++ b/src/cmd/compile/internal/gc/scope_test.go
@@ -202,8 +202,6 @@ var testfile = []testline{
 
 const detailOutput = false
 
-func init() { testenv.SetModVendor() }
-
 // Compiles testfile checks that the description of lexical blocks emitted
 // by the linker in debug_info, for each function in the main package,
 // corresponds to what we expect it to be.
diff --git a/src/cmd/cover/cover_test.go b/src/cmd/cover/cover_test.go
index d7e6ca99b7..f002442b63 100644
--- a/src/cmd/cover/cover_test.go
+++ b/src/cmd/cover/cover_test.go
@@ -77,8 +77,6 @@ var debug = flag.Bool("debug", false, "keep rewritten files for debugging")
 // We use TestMain to set up a temporary directory and remove it when
 // the tests are done.
 func TestMain(m *testing.M) {
-	testenv.SetModVendor()
-
 	dir, err := ioutil.TempDir("", "gotestcover")
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
diff --git a/src/cmd/internal/obj/x86/obj6_test.go b/src/cmd/internal/obj/x86/obj6_test.go
index 2b1a729c8f..c5399744f2 100644
--- a/src/cmd/internal/obj/x86/obj6_test.go
+++ b/src/cmd/internal/obj/x86/obj6_test.go
@@ -134,8 +134,6 @@ func parseOutput(t *testing.T, td *ParsedTestData, asmout []byte) {
 	}
 }
 
-func init() { testenv.SetModVendor() }
-
 func TestDynlink(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 
diff --git a/src/cmd/link/internal/ld/ld_test.go b/src/cmd/link/internal/ld/ld_test.go
index 219b2a63ca..0816429316 100644
--- a/src/cmd/link/internal/ld/ld_test.go
+++ b/src/cmd/link/internal/ld/ld_test.go
@@ -13,8 +13,6 @@ import (
 	"testing"
 )
 
-func init() { testenv.SetModVendor() }
-
 func TestUndefinedRelocErrors(t *testing.T) {
 	t.Parallel()
 	testenv.MustHaveGoBuild(t)
diff --git a/src/cmd/link/link_test.go b/src/cmd/link/link_test.go
index 5043a778ca..5200c3a6f0 100644
--- a/src/cmd/link/link_test.go
+++ b/src/cmd/link/link_test.go
@@ -38,8 +38,6 @@ func TestLargeSymName(t *testing.T) {
 	_ = AuthorPaidByTheColumnInch
 }
 
-func init() { testenv.SetModVendor() }
-
 func TestIssue21703(t *testing.T) {
 	t.Parallel()
 
diff --git a/src/cmd/nm/nm_test.go b/src/cmd/nm/nm_test.go
index 82f4235510..8176ddd7f4 100644
--- a/src/cmd/nm/nm_test.go
+++ b/src/cmd/nm/nm_test.go
@@ -30,8 +30,6 @@ func testMain(m *testing.M) int {
 		return 0
 	}
 
-	testenv.SetModVendor()
-
 	tmpDir, err := ioutil.TempDir("", "TestNM")
 	if err != nil {
 		fmt.Println("TempDir failed:", err)
diff --git a/src/cmd/objdump/objdump_test.go b/src/cmd/objdump/objdump_test.go
index 7c874e853b..be9fe5274a 100644
--- a/src/cmd/objdump/objdump_test.go
+++ b/src/cmd/objdump/objdump_test.go
@@ -24,7 +24,6 @@ func TestMain(m *testing.M) {
 	if !testenv.HasGoBuild() {
 		return
 	}
-	testenv.SetModVendor()
 
 	var exitcode int
 	if err := buildObjdump(); err == nil {
diff --git a/src/cmd/vet/all/main.go b/src/cmd/vet/all/main.go
index 018eba4d6e..6e4a4e297e 100644
--- a/src/cmd/vet/all/main.go
+++ b/src/cmd/vet/all/main.go
@@ -44,7 +44,6 @@ func main() {
 	log.SetPrefix("vet/all: ")
 	log.SetFlags(log.Lshortfile)
 
-	testenv.SetModVendor()
 	var err error
 	cmdGoPath, err = testenv.GoTool()
 	if err != nil {
diff --git a/src/cmd/vet/vet_test.go b/src/cmd/vet/vet_test.go
index 62c28fb9a2..5d8139d977 100644
--- a/src/cmd/vet/vet_test.go
+++ b/src/cmd/vet/vet_test.go
@@ -32,8 +32,6 @@ func TestMain(m *testing.M) {
 }
 
 func testMain(m *testing.M) int {
-	testenv.SetModVendor()
-
 	dir, err := ioutil.TempDir("", "vet_test")
 	if err != nil {
 		fmt.Fprintln(os.Stderr, err)
diff --git a/src/crypto/x509/x509_test.go b/src/crypto/x509/x509_test.go
index fbcdb7b58e..f5851f1f11 100644
--- a/src/crypto/x509/x509_test.go
+++ b/src/crypto/x509/x509_test.go
@@ -1146,8 +1146,6 @@ func TestParsePEMCRL(t *testing.T) {
 	// Can't check the signature here without a package cycle.
 }
 
-func init() { testenv.SetModVendor() }
-
 func TestImports(t *testing.T) {
 	testenv.MustHaveGoRun(t)
 
diff --git a/src/debug/gosym/pclntab_test.go b/src/debug/gosym/pclntab_test.go
index c67fb66f0d..d21f0e24a8 100644
--- a/src/debug/gosym/pclntab_test.go
+++ b/src/debug/gosym/pclntab_test.go
@@ -21,8 +21,6 @@ var (
 	pclinetestBinary string
 )
 
-func init() { testenv.SetModVendor() }
-
 func dotest(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 	// For now, only works on amd64 platforms.
diff --git a/src/go/importer/importer_test.go b/src/go/importer/importer_test.go
index 2887ec6ea5..ff6e12c0da 100644
--- a/src/go/importer/importer_test.go
+++ b/src/go/importer/importer_test.go
@@ -16,8 +16,6 @@ import (
 	"testing"
 )
 
-func init() { testenv.SetModVendor() }
-
 func TestForCompiler(t *testing.T) {
 	testenv.MustHaveGoBuild(t)
 
diff --git a/src/go/internal/srcimporter/srcimporter_test.go b/src/go/internal/srcimporter/srcimporter_test.go
index 06472447a6..b84672610c 100644
--- a/src/go/internal/srcimporter/srcimporter_test.go
+++ b/src/go/internal/srcimporter/srcimporter_test.go
@@ -18,8 +18,6 @@ import (
 	"time"
 )
 
-func init() { testenv.SetModVendor() }
-
 const maxTime = 2 * time.Second
 
 var importer = New(&build.Default, token.NewFileSet(), make(map[string]*types.Package))
diff --git a/src/internal/testenv/testenv.go b/src/internal/testenv/testenv.go
index 72e4d803cb..8f69fe0da5 100644
--- a/src/internal/testenv/testenv.go
+++ b/src/internal/testenv/testenv.go
@@ -19,7 +19,6 @@ import (
 	"runtime"
 	"strconv"
 	"strings"
-	"sync"
 	"testing"
 )
 
@@ -78,31 +77,6 @@ func MustHaveGoRun(t testing.TB) {
 	}
 }
 
-var modVendorOnce sync.Once
-
-// SetModVendor adds the "-mod=vendor" flag to the GOFLAGS environment variable.
-// This allows tests whose working directories are within the cmd and std
-// modules to run ``go'' commands without accessing the network to load
-// dependencies modules.
-//
-// SetModVendor must be called before any test may read the GOFLAGS environment
-// variable.
-//
-// TODO(golang.org/issue/30240): If we load go.mod files from vendor/
-// automatically, this will probably no longer be necessary.
-func SetModVendor() {
-	modVendorOnce.Do(func() {
-		var goflags []string
-		for _, f := range strings.Fields(os.Getenv("GOFLAGS")) {
-			if !strings.HasPrefix(f, "-mod=") && !strings.HasPrefix(f, "--mod=") {
-				goflags = append(goflags, f)
-			}
-		}
-		goflags = append(goflags, "-mod=vendor")
-		os.Setenv("GOFLAGS", strings.Join(goflags, " "))
-	})
-}
-
 // GoToolPath reports the path to the Go tool.
 // It is a convenience wrapper around GoTool.
 // If the tool is unavailable GoToolPath calls t.Skip.
diff --git a/src/runtime/crash_test.go b/src/runtime/crash_test.go
index 3a27b269a1..03ebf022a6 100644
--- a/src/runtime/crash_test.go
+++ b/src/runtime/crash_test.go
@@ -25,8 +25,6 @@ import (
 var toRemove []string
 
 func TestMain(m *testing.M) {
-	testenv.SetModVendor()
-
 	status := m.Run()
 	for _, file := range toRemove {
 		os.RemoveAll(file)
diff --git a/src/runtime/pprof/proto_test.go b/src/runtime/pprof/proto_test.go
index a276d81c49..4452d51231 100644
--- a/src/runtime/pprof/proto_test.go
+++ b/src/runtime/pprof/proto_test.go
@@ -301,8 +301,6 @@ func TestProcSelfMaps(t *testing.T) {
 	})
 }
 
-func init() { testenv.SetModVendor() }
-
 // TestMapping checkes the mapping section of CPU profiles
 // has the HasFunctions field set correctly. If all PCs included
 // in the samples are successfully symbolized, the corresponding