diff --git a/sandbox.go b/sandbox.go
index 346b47b..4f3ed9d 100644
--- a/sandbox.go
+++ b/sandbox.go
@@ -171,6 +171,39 @@
 	return fmt.Sprintf("%s-%s-%x", prefix, runtime.Version(), h.Sum(nil))
 }
 
+// experiments returns the experiments listed in // GOEXPERIMENT=xxx comments
+// at the top of src.
+func experiments(src string) []string {
+	var exp []string
+	for src != "" {
+		line := src
+		src = ""
+		if i := strings.Index(line, "\n"); i >= 0 {
+			line, src = line[:i], line[i+1:]
+		}
+		line = strings.TrimSpace(line)
+		if line == "" {
+			continue
+		}
+		if !strings.HasPrefix(line, "//") {
+			break
+		}
+		line = strings.TrimSpace(strings.TrimPrefix(line, "//"))
+		if !strings.HasPrefix(line, "GOEXPERIMENT") {
+			continue
+		}
+		line = strings.TrimSpace(strings.TrimPrefix(line, "GOEXPERIMENT"))
+		if !strings.HasPrefix(line, "=") {
+			continue
+		}
+		line = strings.TrimSpace(strings.TrimPrefix(line, "="))
+		if line != "" {
+			exp = append(exp, line)
+		}
+	}
+	return exp
+}
+
 // isTestFunc tells whether fn has the type of a testing, or fuzz function, or a TestMain func.
 func isTestFunc(fn *ast.FuncDecl) bool {
 	if fn.Type.Results != nil && len(fn.Type.Results.List) > 0 ||
@@ -371,6 +404,7 @@
 		files.AddFile("go.mod", []byte("module play\n"))
 	}
 
+	var exp []string
 	for f, src := range files.m {
 		// Before multi-file support we required that the
 		// program be in package main, so continue to do that
@@ -382,6 +416,7 @@
 			if err == nil && f.Name.Name != "main" {
 				return &buildResult{errorMessage: "package name must be main"}, nil
 			}
+			exp = append(exp, experiments(string(src))...)
 		}
 
 		in := filepath.Join(tmpDir, f)
@@ -421,6 +456,7 @@
 	cmd.Env = []string{"GOOS=linux", "GOARCH=amd64", "GOROOT=/usr/local/go-faketime"}
 	cmd.Env = append(cmd.Env, "GOCACHE="+goCache)
 	cmd.Env = append(cmd.Env, "CGO_ENABLED=0")
+	cmd.Env = append(cmd.Env, "GOEXPERIMENT="+strings.Join(exp, ","))
 	// Create a GOPATH just for modules to be downloaded
 	// into GOPATH/pkg/mod.
 	cmd.Args = append(cmd.Args, "-modcacherw")
diff --git a/sandbox_test.go b/sandbox_test.go
index de390bf..6130936 100644
--- a/sandbox_test.go
+++ b/sandbox_test.go
@@ -14,6 +14,28 @@
 	"testing"
 )
 
+// TestExperiments tests that experiment lines are recognized.
+func TestExperiments(t *testing.T) {
+	var tests = []struct {
+		src string
+		exp []string
+	}{
+		{"//GOEXPERIMENT=active\n\npackage main", []string{"active"}},
+		{"   //   GOEXPERIMENT=   active   \n\npackage main", []string{"active"}},
+		{"   //   GOEXPERIMENT=   active   \n\npackage main", []string{"active"}},
+		{"   //   GOEXPERIMENT   =   active   \n\npackage main", []string{"active"}},
+		{"//GOEXPERIMENT=foo\n\n// GOEXPERIMENT=bar\n\npackage main", []string{"foo", "bar"}},
+		{"/* hello world */\n// GOEXPERIMENT=ignored\n", nil},
+		{"package main\n// GOEXPERIMENT=ignored\n", nil},
+	}
+
+	for _, tt := range tests {
+		if exp := experiments(tt.src); !reflect.DeepEqual(exp, tt.exp) {
+			t.Errorf("experiments(%q) = %q, want %q", tt.src, exp, tt.exp)
+		}
+	}
+}
+
 // TestIsTest verifies that the isTest helper function matches
 // exactly (and only) the names of functions recognized as tests.
 func TestIsTest(t *testing.T) {