diff --git a/src/context/benchmark_test.go b/src/context/benchmark_test.go
index 3c526dd106..6dd8510ff4 100644
--- a/src/context/benchmark_test.go
+++ b/src/context/benchmark_test.go
@@ -96,3 +96,21 @@ func buildContextTree(root Context, depth int) {
 		root, _ = WithCancel(root)
 	}
 }
+
+func BenchmarkCheckCanceled(b *testing.B) {
+	ctx, cancel := WithCancel(Background())
+	cancel()
+	b.Run("Err", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			ctx.Err()
+		}
+	})
+	b.Run("Done", func(b *testing.B) {
+		for i := 0; i < b.N; i++ {
+			select {
+			case <-ctx.Done():
+			default:
+			}
+		}
+	})
+}
diff --git a/src/context/context.go b/src/context/context.go
index 06580e0465..1b4fa41b8c 100644
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -334,8 +334,9 @@ func (c *cancelCtx) Done() <-chan struct{} {
 
 func (c *cancelCtx) Err() error {
 	c.mu.Lock()
-	defer c.mu.Unlock()
-	return c.err
+	err := c.err
+	c.mu.Unlock()
+	return err
 }
 
 func (c *cancelCtx) String() string {