diff --git a/src/cmd/go/internal/work/init.go b/src/cmd/go/internal/work/init.go
index e970272954..a574924c5b 100644
--- a/src/cmd/go/internal/work/init.go
+++ b/src/cmd/go/internal/work/init.go
@@ -10,6 +10,7 @@ import (
 	"cmd/go/internal/base"
 	"cmd/go/internal/cfg"
 	"cmd/go/internal/load"
+	"cmd/internal/objabi"
 	"cmd/internal/sys"
 	"flag"
 	"fmt"
@@ -34,6 +35,20 @@ func BuildInit() {
 		}
 		cfg.BuildPkgdir = p
 	}
+
+	// For each experiment that has been enabled in the toolchain, define a
+	// build tag with the same name but prefixed by "goexperiment." which can be
+	// used for compiling alternative files for the experiment. This allows
+	// changes for the experiment, like extra struct fields in the runtime,
+	// without affecting the base non-experiment code at all. [2:] strips the
+	// leading "X:" from objabi.Expstring().
+	exp := objabi.Expstring()[2:]
+	if exp != "none" {
+		experiments := strings.Split(exp, ",")
+		for _, expt := range experiments {
+			cfg.BuildContext.BuildTags = append(cfg.BuildContext.BuildTags, "goexperiment."+expt)
+		}
+	}
 }
 
 func instrumentInit() {
diff --git a/src/cmd/go/script_test.go b/src/cmd/go/script_test.go
index 3eb66f9166..87afb6aec8 100644
--- a/src/cmd/go/script_test.go
+++ b/src/cmd/go/script_test.go
@@ -30,6 +30,7 @@ import (
 	"cmd/go/internal/robustio"
 	"cmd/go/internal/txtar"
 	"cmd/go/internal/work"
+	"cmd/internal/objabi"
 	"cmd/internal/sys"
 )
 
@@ -119,6 +120,7 @@ func (ts *testScript) setup() {
 		"GOCACHE=" + testGOCACHE,
 		"GODEBUG=" + os.Getenv("GODEBUG"),
 		"GOEXE=" + cfg.ExeSuffix,
+		"GOEXPSTRING=" + objabi.Expstring()[2:],
 		"GOOS=" + runtime.GOOS,
 		"GOPATH=" + filepath.Join(ts.workdir, "gopath"),
 		"GOPROXY=" + proxyURL,
diff --git a/src/cmd/go/testdata/script/README b/src/cmd/go/testdata/script/README
index 81b6d9d814..f4c92e65ab 100644
--- a/src/cmd/go/testdata/script/README
+++ b/src/cmd/go/testdata/script/README
@@ -29,6 +29,7 @@ Scripts also have access to these other environment variables:
 	GOARCH=<target GOARCH>
 	GOCACHE=<actual GOCACHE being used outside the test>
 	GOEXE=<executable file suffix: .exe on Windows, empty on other systems>
+	GOEXPSTRING=<value of objabi.Expstring(), from GOEXPERIMENT when toolchain built>
 	GOOS=<target GOOS>
 	GOPATH=$WORK/gopath
 	GOPROXY=<local module proxy serving from cmd/go/testdata/mod>
diff --git a/src/cmd/go/testdata/script/build_tag_goexperiment.txt b/src/cmd/go/testdata/script/build_tag_goexperiment.txt
new file mode 100644
index 0000000000..26ad029845
--- /dev/null
+++ b/src/cmd/go/testdata/script/build_tag_goexperiment.txt
@@ -0,0 +1,104 @@
+# compile_ext will fail if the buildtags that are enabled (or not enabled) for the
+# framepointer and fieldtrack experiments are not consistent with the value of
+# GOEXPSTRING (which comes from objabi.Expstring()).
+
+[short] skip
+go run m
+
+-- expt_main.go --
+package main
+
+import (
+	"os"
+	"strings"
+)
+
+func main() {
+  fp()
+  ft()
+}
+
+func hasExpEntry(s string) bool {
+	// script_test.go defines GOEXPSTRING to be the value of
+	// objabi.Expstring(), which gives the enabled experiments baked into the
+	// toolchain.
+	g := os.Getenv("GOEXPSTRING")
+	for _, f := range strings.Split(g, ",") {
+		if f == s {
+			return true
+		}
+	}
+	return false
+}
+
+-- fp_off.go --
+// +build !goexperiment.framepointer
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func fp() {
+	if hasExpEntry("framepointer") {
+		fmt.Println("in !framepointer build, but objabi.Expstring() has 'framepointer'")
+		os.Exit(1)
+	}
+}
+
+-- fp_on.go --
+// +build goexperiment.framepointer
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func fp() {
+	if !hasExpEntry("framepointer") {
+		fmt.Println("in framepointer build, but objabi.Expstring() does not have 'framepointer', is", os.Getenv("GOEXPSTRING"))
+		os.Exit(1)
+	}
+}
+
+-- ft_off.go --
+// +build !goexperiment.fieldtrack
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func ft() {
+	if hasExpEntry("fieldtrack") {
+		fmt.Println("in !fieldtrack build, but objabi.Expstring() has 'fieldtrack'")
+		os.Exit(1)
+	}
+}
+
+-- ft_on.go --
+// +build goexperiment.fieldtrack
+
+package main
+
+import (
+	"fmt"
+	"os"
+)
+
+func ft() {
+	if !hasExpEntry("fieldtrack") {
+		fmt.Println("in fieldtrack build, but objabi.Expstring() does not have 'fieldtrack', is", os.Getenv("GOEXPSTRING"))
+		os.Exit(1)
+	}
+}
+
+-- go.mod --
+module m
+go 1.14