diff --git a/balancer/base/balancer.go b/balancer/base/balancer.go
index b0fa5192161..a7f1eeec8e6 100644
--- a/balancer/base/balancer.go
+++ b/balancer/base/balancer.go
@@ -105,7 +105,12 @@ func (b *baseBalancer) UpdateClientConnState(s balancer.ClientConnState) error {
 		addrsSet.Set(a, nil)
 		if _, ok := b.subConns.Get(a); !ok {
 			// a is a new address (not existing in b.subConns).
-			sc, err := b.cc.NewSubConn([]resolver.Address{a}, balancer.NewSubConnOptions{HealthCheckEnabled: b.config.HealthCheck})
+			var sc balancer.SubConn
+			opts := balancer.NewSubConnOptions{
+				HealthCheckEnabled: b.config.HealthCheck,
+				StateListener:      func(scs balancer.SubConnState) { b.updateSubConnState(sc, scs) },
+			}
+			sc, err := b.cc.NewSubConn([]resolver.Address{a}, opts)
 			if err != nil {
 				logger.Warningf("base.baseBalancer: failed to create new SubConn: %v", err)
 				continue
@@ -124,7 +129,7 @@ func (b *baseBalancer) UpdateClientConnState(s balancer.ClientConnState) error {
 			sc.Shutdown()
 			b.subConns.Delete(a)
 			// Keep the state of this sc in b.scStates until sc's state becomes Shutdown.
-			// The entry will be deleted in UpdateSubConnState.
+			// The entry will be deleted in updateSubConnState.
 		}
 	}
 	// If resolver state contains no addresses, return an error so ClientConn
@@ -177,7 +182,12 @@ func (b *baseBalancer) regeneratePicker() {
 	b.picker = b.pickerBuilder.Build(PickerBuildInfo{ReadySCs: readySCs})
 }
 
+// UpdateSubConnState is a nop because a StateListener is always set in NewSubConn.
 func (b *baseBalancer) UpdateSubConnState(sc balancer.SubConn, state balancer.SubConnState) {
+	logger.Errorf("base.baseBalancer: UpdateSubConnState(%v, %+v) called unexpectedly", sc, state)
+}
+
+func (b *baseBalancer) updateSubConnState(sc balancer.SubConn, state balancer.SubConnState) {
 	s := state.ConnectivityState
 	if logger.V(2) {
 		logger.Infof("base.baseBalancer: handle SubConn state change: %p, %v", sc, s)
diff --git a/balancer/base/balancer_test.go b/balancer/base/balancer_test.go
index 7bf4d92f8f0..8a97b4220a5 100644
--- a/balancer/base/balancer_test.go
+++ b/balancer/base/balancer_test.go
@@ -19,7 +19,9 @@
 package base
 
 import (
+	"context"
 	"testing"
+	"time"
 
 	"google.golang.org/grpc/attributes"
 	"google.golang.org/grpc/balancer"
@@ -38,7 +40,9 @@ func (c *testClientConn) NewSubConn(addrs []resolver.Address, opts balancer.NewS
 
 func (c *testClientConn) UpdateState(balancer.State) {}
 
-type testSubConn struct{}
+type testSubConn struct {
+	updateState func(balancer.SubConnState)
+}
 
 func (sc *testSubConn) UpdateAddresses(addresses []resolver.Address) {}
 
@@ -61,7 +65,11 @@ func (p *testPickBuilder) Build(info PickerBuildInfo) balancer.Picker {
 }
 
 func TestBaseBalancerReserveAttributes(t *testing.T) {
-	var v = func(info PickerBuildInfo) {
+	ctx, cancel := context.WithTimeout(context.Background(), 10*time.Second)
+	defer cancel()
+	validated := make(chan struct{}, 1)
+	v := func(info PickerBuildInfo) {
+		defer func() { validated <- struct{}{} }()
 		for _, sc := range info.ReadySCs {
 			if sc.Address.Addr == "1.1.1.1" {
 				if sc.Address.Attributes == nil {
@@ -80,8 +88,8 @@ func TestBaseBalancerReserveAttributes(t *testing.T) {
 	}
 	pickBuilder := &testPickBuilder{validate: v}
 	b := (&baseBuilder{pickerBuilder: pickBuilder}).Build(&testClientConn{
-		newSubConn: func(addrs []resolver.Address, _ balancer.NewSubConnOptions) (balancer.SubConn, error) {
-			return &testSubConn{}, nil
+		newSubConn: func(addrs []resolver.Address, opts balancer.NewSubConnOptions) (balancer.SubConn, error) {
+			return &testSubConn{updateState: opts.StateListener}, nil
 		},
 	}, balancer.BuildOptions{}).(*baseBalancer)
 
@@ -93,8 +101,18 @@ func TestBaseBalancerReserveAttributes(t *testing.T) {
 			},
 		},
 	})
+	select {
+	case <-validated:
+	case <-ctx.Done():
+		t.Fatalf("timed out waiting for UpdateClientConnState to call picker.Build")
+	}
 
 	for sc := range b.scStates {
-		b.UpdateSubConnState(sc, balancer.SubConnState{ConnectivityState: connectivity.Ready, ConnectionError: nil})
+		sc.(*testSubConn).updateState(balancer.SubConnState{ConnectivityState: connectivity.Ready, ConnectionError: nil})
+		select {
+		case <-validated:
+		case <-ctx.Done():
+			t.Fatalf("timed out waiting for UpdateClientConnState to call picker.Build")
+		}
 	}
 }