diff --git a/gopls/internal/regtest/codelens/codelens_test.go b/gopls/internal/regtest/codelens/codelens_test.go
index ad35a299114..38721fb2c60 100644
--- a/gopls/internal/regtest/codelens/codelens_test.go
+++ b/gopls/internal/regtest/codelens/codelens_test.go
@@ -292,6 +292,13 @@ func TestGCDetails(t *testing.T) {
 		t.Skipf("the gc details code lens doesn't work on Android")
 	}
 
+	// TestGCDetails seems to suffer from poor performance on certain builders.
+	// Give it as long as it needs to complete.
+	timeout := 60 * time.Second
+	if d, ok := testenv.Deadline(t); ok {
+		timeout = time.Until(d) * 19 / 20 // Leave 5% headroom for cleanup.
+	}
+
 	const mod = `
 -- go.mod --
 module mod.com
@@ -311,8 +318,7 @@ func main() {
 			CodeLenses: map[string]bool{
 				"gc_details": true,
 			}},
-		// TestGCDetails seems to suffer from poor performance on certain builders. Give it some more time to complete.
-		Timeout(60*time.Second),
+		Timeout(timeout),
 	).Run(t, mod, func(t *testing.T, env *Env) {
 		env.OpenFile("main.go")
 		env.ExecuteCodeLensCommand("main.go", command.GCDetails)
diff --git a/internal/testenv/testenv.go b/internal/testenv/testenv.go
index 2a7b2a6a6dd..b3812326499 100644
--- a/internal/testenv/testenv.go
+++ b/internal/testenv/testenv.go
@@ -15,6 +15,7 @@ import (
 	"runtime"
 	"strings"
 	"sync"
+	"time"
 
 	exec "golang.org/x/sys/execabs"
 )
@@ -307,3 +308,15 @@ func SkipAfterGo1Point(t Testing, x int) {
 		t.Skipf("running Go version %q is version 1.%d, newer than maximum 1.%d", runtime.Version(), Go1Point(), x)
 	}
 }
+
+// Deadline returns the deadline of t, if known,
+// using the Deadline method added in Go 1.15.
+func Deadline(t Testing) (time.Time, bool) {
+	td, ok := t.(interface {
+		Deadline() (time.Time, bool)
+	})
+	if !ok {
+		return time.Time{}, false
+	}
+	return td.Deadline()
+}