diff --git a/misc/reboot/experiment_toolid_test.go b/misc/reboot/experiment_toolid_test.go
new file mode 100644
index 0000000000..eabf06b19e
--- /dev/null
+++ b/misc/reboot/experiment_toolid_test.go
@@ -0,0 +1,101 @@
+// Copyright 2019 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// +build explicit
+
+// Package experiment_toolid_test verifies that GOEXPERIMENT settings built
+// into the toolchain influence tool ids in the Go command.
+// This test requires bootstrapping the toolchain twice, so it's very expensive.
+// It must be run explicitly with -tags=explicit.
+// Verifies golang.org/issue/33091.
+package reboot_test
+
+import (
+	"bytes"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"runtime"
+	"testing"
+)
+
+func TestExperimentToolID(t *testing.T) {
+	// Set up GOROOT
+	goroot, err := ioutil.TempDir("", "experiment-goroot")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(goroot)
+
+	gorootSrc := filepath.Join(goroot, "src")
+	if err := overlayDir(gorootSrc, filepath.Join(runtime.GOROOT(), "src")); err != nil {
+		t.Fatal(err)
+	}
+
+	if err := ioutil.WriteFile(filepath.Join(goroot, "VERSION"), []byte("go1.999"), 0666); err != nil {
+		t.Fatal(err)
+	}
+	env := append(os.Environ(), "GOROOT=", "GOROOT_BOOTSTRAP="+runtime.GOROOT())
+
+	// Use a clean cache.
+	gocache, err := ioutil.TempDir("", "experiment-gocache")
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.RemoveAll(gocache)
+	env = append(env, "GOCACHE="+gocache)
+
+	// Build the toolchain without GOEXPERIMENT.
+	var makeScript string
+	switch runtime.GOOS {
+	case "windows":
+		makeScript = "make.bat"
+	case "plan9":
+		makeScript = "make.rc"
+	default:
+		makeScript = "make.bash"
+	}
+	makeScriptPath := filepath.Join(runtime.GOROOT(), "src", makeScript)
+	runCmd(t, gorootSrc, env, makeScriptPath)
+
+	// Verify compiler version string.
+	goCmdPath := filepath.Join(goroot, "bin", "go")
+	if runtime.GOOS == "windows" {
+		goCmdPath += ".exe"
+	}
+	gotVersion := bytes.TrimSpace(runCmd(t, gorootSrc, env, goCmdPath, "tool", "compile", "-V=full"))
+	wantVersion := []byte(`compile version go1.999`)
+	if !bytes.Equal(gotVersion, wantVersion) {
+		t.Errorf("compile version without experiment: got %q, want %q", gotVersion, wantVersion)
+	}
+
+	// Build a package in a mode not handled by the make script.
+	runCmd(t, gorootSrc, env, goCmdPath, "build", "-race", "archive/tar")
+
+	// Rebuild the toolchain with GOEXPERIMENT.
+	env = append(env, "GOEXPERIMENT=fieldtrack")
+	runCmd(t, gorootSrc, env, makeScriptPath)
+
+	// Verify compiler version string.
+	gotVersion = bytes.TrimSpace(runCmd(t, gorootSrc, env, goCmdPath, "tool", "compile", "-V=full"))
+	wantVersion = []byte(`compile version go1.999 X:fieldtrack,framepointer`)
+	if !bytes.Equal(gotVersion, wantVersion) {
+		t.Errorf("compile version with experiment: got %q, want %q", gotVersion, wantVersion)
+	}
+
+	// Build the same package. We should not get a cache conflict.
+	runCmd(t, gorootSrc, env, goCmdPath, "build", "-race", "archive/tar")
+}
+
+func runCmd(t *testing.T, dir string, env []string, path string, args ...string) []byte {
+	cmd := exec.Command(path, args...)
+	cmd.Dir = dir
+	cmd.Env = env
+	out, err := cmd.Output()
+	if err != nil {
+		t.Fatal(err)
+	}
+	return out
+}
diff --git a/src/cmd/go/internal/work/buildid.go b/src/cmd/go/internal/work/buildid.go
index 1f6d1e8e77..bf485d75ad 100644
--- a/src/cmd/go/internal/work/buildid.go
+++ b/src/cmd/go/internal/work/buildid.go
@@ -203,8 +203,9 @@ func (b *Builder) toolID(name string) string {
 		// On the development branch, use the content ID part of the build ID.
 		id = contentID(f[len(f)-1])
 	} else {
-		// For a release, the output is like: "compile version go1.9.1". Use the whole line.
-		id = f[2]
+		// For a release, the output is like: "compile version go1.9.1 X:framepointer".
+		// Use the whole line.
+		id = strings.TrimSpace(line)
 	}
 
 	b.id.Lock()
diff --git a/src/cmd/internal/objabi/flag.go b/src/cmd/internal/objabi/flag.go
index 90e944656b..79ad2ccf74 100644
--- a/src/cmd/internal/objabi/flag.go
+++ b/src/cmd/internal/objabi/flag.go
@@ -86,6 +86,10 @@ func (versionFlag) Set(s string) error {
 	name = name[strings.LastIndex(name, `/`)+1:]
 	name = name[strings.LastIndex(name, `\`)+1:]
 	name = strings.TrimSuffix(name, ".exe")
+
+	// If there's an active experiment, include that,
+	// to distinguish go1.10.2 with an experiment
+	// from go1.10.2 without an experiment.
 	p := Expstring()
 	if p == DefaultExpstring() {
 		p = ""
@@ -101,12 +105,6 @@ func (versionFlag) Set(s string) error {
 	// build ID of the binary, so that if the compiler is changed and
 	// rebuilt, we notice and rebuild all packages.
 	if s == "full" {
-		// If there's an active experiment, include that,
-		// to distinguish go1.10.2 with an experiment
-		// from go1.10.2 without an experiment.
-		if x := Expstring(); x != "" {
-			p += " " + x
-		}
 		if strings.HasPrefix(Version, "devel") {
 			p += " buildID=" + buildID
 		}