diff --git a/balancer/balancer.go b/balancer/balancer.go
index 3a2092f1056e..324915c1692f 100644
--- a/balancer/balancer.go
+++ b/balancer/balancer.go
@@ -155,6 +155,9 @@ type SubConn interface {
 	// indicate the shutdown operation.  This may be delivered before
 	// in-progress RPCs are complete and the actual connection is closed.
 	Shutdown()
+	// enforceEmbedding is an unexported method to force implementers embed
+	// this interface, allowing gRPC to add methods without breaking users.
+	enforceEmbedding()
 }
 
 // NewSubConnOptions contains options to create new SubConn.
diff --git a/balancer/base/balancer_test.go b/balancer/base/balancer_test.go
index ea868f29245d..ea4a4fda2493 100644
--- a/balancer/base/balancer_test.go
+++ b/balancer/base/balancer_test.go
@@ -41,6 +41,7 @@ func (c *testClientConn) NewSubConn(addrs []resolver.Address, opts balancer.NewS
 func (c *testClientConn) UpdateState(balancer.State) {}
 
 type testSubConn struct {
+	balancer.SubConn
 	updateState func(balancer.SubConnState)
 }
 
diff --git a/balancer_wrapper.go b/balancer_wrapper.go
index 2a4f2878aef4..80620d31093d 100644
--- a/balancer_wrapper.go
+++ b/balancer_wrapper.go
@@ -254,6 +254,7 @@ func (ccb *ccBalancerWrapper) Target() string {
 // acBalancerWrapper is a wrapper on top of ac for balancers.
 // It implements balancer.SubConn interface.
 type acBalancerWrapper struct {
+	balancer.SubConn
 	ac            *addrConn          // read-only
 	ccb           *ccBalancerWrapper // read-only
 	stateListener func(balancer.SubConnState)
diff --git a/internal/testutils/balancer.go b/internal/testutils/balancer.go
index 80021903df3c..423e8d25f2f2 100644
--- a/internal/testutils/balancer.go
+++ b/internal/testutils/balancer.go
@@ -32,6 +32,7 @@ import (
 
 // TestSubConn implements the SubConn interface, to be used in tests.
 type TestSubConn struct {
+	balancer.SubConn
 	tcc           *BalancerClientConn // the CC that owns this SubConn
 	id            string
 	ConnectCh     chan struct{}