diff --git a/src/context/context.go b/src/context/context.go
index e40b63ef3cd..3afa3e90d2c 100644
--- a/src/context/context.go
+++ b/src/context/context.go
@@ -252,9 +252,9 @@ func propagateCancel(parent Context, child canceler) {
 			child.cancel(false, p.err)
 		} else {
 			if p.children == nil {
-				p.children = make(map[canceler]bool)
+				p.children = make(map[canceler]struct{})
 			}
-			p.children[child] = true
+			p.children[child] = struct{}{}
 		}
 		p.mu.Unlock()
 	} else {
@@ -314,8 +314,8 @@ type cancelCtx struct {
 	done chan struct{} // closed by the first cancel call.
 
 	mu       sync.Mutex
-	children map[canceler]bool // set to nil by the first cancel call
-	err      error             // set to non-nil by the first cancel call
+	children map[canceler]struct{} // set to nil by the first cancel call
+	err      error                 // set to non-nil by the first cancel call
 }
 
 func (c *cancelCtx) Done() <-chan struct{} {
diff --git a/src/context/context_test.go b/src/context/context_test.go
index c31c4d8718d..d305db50dc0 100644
--- a/src/context/context_test.go
+++ b/src/context/context_test.go
@@ -92,6 +92,11 @@ func TestWithCancel(t *testing.T) {
 	}
 }
 
+func contains(m map[canceler]struct{}, key canceler) bool {
+	_, ret := m[key]
+	return ret
+}
+
 func TestParentFinishesChild(t *testing.T) {
 	// Context tree:
 	// parent -> cancelChild
@@ -120,7 +125,7 @@ func TestParentFinishesChild(t *testing.T) {
 	cc := cancelChild.(*cancelCtx)
 	tc := timerChild.(*timerCtx)
 	pc.mu.Lock()
-	if len(pc.children) != 2 || !pc.children[cc] || !pc.children[tc] {
+	if len(pc.children) != 2 || !contains(pc.children, cc) || !contains(pc.children, tc) {
 		t.Errorf("bad linkage: pc.children = %v, want %v and %v",
 			pc.children, cc, tc)
 	}
@@ -191,7 +196,7 @@ func TestChildFinishesFirst(t *testing.T) {
 
 		if pcok {
 			pc.mu.Lock()
-			if len(pc.children) != 1 || !pc.children[cc] {
+			if len(pc.children) != 1 || !contains(pc.children, cc) {
 				t.Errorf("bad linkage: pc.children = %v, cc = %v", pc.children, cc)
 			}
 			pc.mu.Unlock()
@@ -627,3 +632,36 @@ func TestDeadlineExceededSupportsTimeout(t *testing.T) {
 		t.Fatal("wrong value for timeout")
 	}
 }
+
+func BenchmarkContextCancelTree(b *testing.B) {
+	depths := []int{1, 10, 100, 1000}
+	for _, d := range depths {
+		b.Run(fmt.Sprintf("depth=%d", d), func(b *testing.B) {
+			b.Run("Root=Background", func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					buildContextTree(Background(), d)
+				}
+			})
+			b.Run("Root=OpenCanceler", func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					ctx, cancel := WithCancel(Background())
+					buildContextTree(ctx, d)
+					cancel()
+				}
+			})
+			b.Run("Root=ClosedCanceler", func(b *testing.B) {
+				for i := 0; i < b.N; i++ {
+					ctx, cancel := WithCancel(Background())
+					cancel()
+					buildContextTree(ctx, d)
+				}
+			})
+		})
+	}
+}
+
+func buildContextTree(root Context, depth int) {
+	for d := 0; d < depth; d++ {
+		root, _ = WithCancel(root)
+	}
+}