diff --git a/driver.go b/driver.go
index 75deb480..dee75315 100644
--- a/driver.go
+++ b/driver.go
@@ -25,7 +25,6 @@ import (
 	"strconv"
 	"strings"
 	"sync"
-	"sync/atomic"
 	"time"
 
 	"cloud.google.com/go/civil"
@@ -156,6 +155,9 @@ type connector struct {
 	dsn             string
 	connectorConfig connectorConfig
 
+	closerMu sync.RWMutex
+	closed   bool
+
 	// spannerClientConfig represents the optional advanced configuration to be used
 	// by the Google Cloud Spanner client.
 	spannerClientConfig spanner.ClientConfig
@@ -169,7 +171,7 @@ type connector struct {
 	// propagated to the caller. This option is enabled by default.
 	retryAbortsInternally bool
 
-	initClient     sync.Once
+	initClient     sync.Mutex
 	client         *spanner.Client
 	clientErr      error
 	adminClient    *adminapi.DatabaseAdminClient
@@ -264,6 +266,7 @@ func newConnector(d *Driver, dsn string) (*connector, error) {
 		}
 	}
 	config.UserAgent = userAgent
+
 	c := &connector{
 		driver:                d,
 		dsn:                   dsn,
@@ -277,6 +280,11 @@ func newConnector(d *Driver, dsn string) (*connector, error) {
 }
 
 func (c *connector) Connect(ctx context.Context) (driver.Conn, error) {
+	c.closerMu.RLock()
+	defer c.closerMu.RUnlock()
+	if c.closed {
+		return nil, fmt.Errorf("connector has been closed")
+	}
 	return openDriverConn(ctx, c)
 }
 
@@ -288,17 +296,10 @@ func openDriverConn(ctx context.Context, c *connector) (driver.Conn, error) {
 		c.connectorConfig.instance,
 		c.connectorConfig.database)
 
-	c.initClient.Do(func() {
-		c.client, c.clientErr = spanner.NewClientWithConfig(ctx, databaseName, c.spannerClientConfig, opts...)
-		c.adminClient, c.adminClientErr = adminapi.NewDatabaseAdminClient(ctx, opts...)
-	})
-	if c.clientErr != nil {
-		return nil, c.clientErr
-	}
-	if c.adminClientErr != nil {
-		return nil, c.adminClientErr
+	if err := c.increaseConnCount(ctx, databaseName, opts); err != nil {
+		return nil, err
 	}
-	atomic.AddInt32(&c.connCount, 1)
+
 	return &conn{
 		connector:                  c,
 		client:                     c.client,
@@ -311,10 +312,80 @@ func openDriverConn(ctx context.Context, c *connector) (driver.Conn, error) {
 	}, nil
 }
 
+// increaseConnCount initializes the client and increases the number of connections that are active.
+func (c *connector) increaseConnCount(ctx context.Context, databaseName string, opts []option.ClientOption) error {
+	c.initClient.Lock()
+	defer c.initClient.Unlock()
+
+	if c.clientErr != nil {
+		return c.clientErr
+	}
+	if c.adminClientErr != nil {
+		return c.adminClientErr
+	}
+
+	if c.client == nil {
+		c.client, c.clientErr = spanner.NewClientWithConfig(ctx, databaseName, c.spannerClientConfig, opts...)
+		if c.clientErr != nil {
+			return c.clientErr
+		}
+
+		c.adminClient, c.adminClientErr = adminapi.NewDatabaseAdminClient(ctx, opts...)
+		if c.adminClientErr != nil {
+			c.client = nil
+			c.client.Close()
+			c.adminClient = nil
+			return c.adminClientErr
+		}
+	}
+
+	c.connCount++
+	return nil
+}
+
+// decreaseConnCount decreases the number of connections that are active and closes the underlying clients if it was the
+// last connection.
+func (c *connector) decreaseConnCount() error {
+	c.initClient.Lock()
+	defer c.initClient.Unlock()
+
+	c.connCount--
+	if c.connCount > 0 {
+		return nil
+	}
+
+	return c.closeClients()
+}
+
 func (c *connector) Driver() driver.Driver {
 	return c.driver
 }
 
+func (c *connector) Close() error {
+	c.closerMu.Lock()
+	c.closed = true
+	c.closerMu.Unlock()
+
+	c.driver.mu.Lock()
+	delete(c.driver.connectors, c.dsn)
+	c.driver.mu.Unlock()
+
+	return c.closeClients()
+}
+
+// Closes the underlying clients.
+func (c *connector) closeClients() (err error) {
+	if c.client != nil {
+		c.client.Close()
+		c.client = nil
+	}
+	if c.adminClient != nil {
+		err = c.adminClient.Close()
+		c.adminClient = nil
+	}
+	return err
+}
+
 // SpannerConn is the public interface for the raw Spanner connection for the
 // sql driver. This interface can be used with the db.Conn().Raw() method.
 type SpannerConn interface {
@@ -954,18 +1025,7 @@ func (c *conn) ExecContext(ctx context.Context, query string, args []driver.Name
 }
 
 func (c *conn) Close() error {
-	// Check if this is the last open connection of the connector.
-	if count := atomic.AddInt32(&c.connector.connCount, -1); count > 0 {
-		return nil
-	}
-
-	// This was the last connection. Remove the connector and close the Spanner clients.
-	c.connector.driver.mu.Lock()
-	delete(c.connector.driver.connectors, c.connector.dsn)
-	c.connector.driver.mu.Unlock()
-
-	c.client.Close()
-	return c.adminClient.Close()
+	return c.connector.decreaseConnCount()
 }
 
 func (c *conn) Begin() (driver.Tx, error) {
diff --git a/driver_with_mockserver_test.go b/driver_with_mockserver_test.go
index 901c1548..81e1b0d3 100644
--- a/driver_with_mockserver_test.go
+++ b/driver_with_mockserver_test.go
@@ -2372,7 +2372,118 @@ func TestExcludeTxnFromChangeStreams_Transaction(t *testing.T) {
 	if g, w := exclude, false; g != w {
 		t.Fatalf("exclude_txn_from_change_streams mismatch\n Got: %v\nWant: %v", g, w)
 	}
+}
+
+func TestMaxIdleConnectionsNonZero(t *testing.T) {
+	t.Parallel()
+
+	// Set MinSessions=1, so we can use the number of BatchCreateSessions requests as an indication
+	// of the number of clients that was created.
+	db, server, teardown := setupTestDBConnectionWithParams(t, "MinSessions=1")
+	defer teardown()
+
+	db.SetMaxIdleConns(2)
+	for i := 0; i < 2; i++ {
+		openAndCloseConn(t, db)
+	}
+
+	// Verify that only one client was created.
+	// This happens because we have a non-zero value for the number of idle connections.
+	requests := drainRequestsFromServer(server.TestSpanner)
+	batchRequests := requestsOfType(requests, reflect.TypeOf(&sppb.BatchCreateSessionsRequest{}))
+	if g, w := len(batchRequests), 1; g != w {
+		t.Fatalf("BatchCreateSessions requests count mismatch\n Got: %v\nWant: %v", g, w)
+	}
+}
+
+func TestMaxIdleConnectionsZero(t *testing.T) {
+	t.Parallel()
+
+	// Set MinSessions=1, so we can use the number of BatchCreateSessions requests as an indication
+	// of the number of clients that was created.
+	db, server, teardown := setupTestDBConnectionWithParams(t, "MinSessions=1")
+	defer teardown()
+
+	db.SetMaxIdleConns(0)
+	for i := 0; i < 2; i++ {
+		openAndCloseConn(t, db)
+	}
+
+	// Verify that two clients were created and closed.
+	// This should happen because we do not keep any idle connections open.
+	requests := drainRequestsFromServer(server.TestSpanner)
+	batchRequests := requestsOfType(requests, reflect.TypeOf(&sppb.BatchCreateSessionsRequest{}))
+	if g, w := len(batchRequests), 2; g != w {
+		t.Fatalf("BatchCreateSessions requests count mismatch\n Got: %v\nWant: %v", g, w)
+	}
+}
 
+func openAndCloseConn(t *testing.T, db *sql.DB) {
+	ctx := context.Background()
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatalf("failed to get a connection: %v", err)
+	}
+	defer func() {
+		err = conn.Close()
+		if err != nil {
+			t.Fatalf("failed to close connection: %v", err)
+		}
+	}()
+
+	var result int64
+	if err := conn.QueryRowContext(ctx, "SELECT 1").Scan(&result); err != nil {
+		t.Fatalf("failed to select: %v", err)
+	}
+	if result != 1 {
+		t.Fatalf("expected 1 got %v", result)
+	}
+}
+
+func TestCannotReuseClosedConnector(t *testing.T) {
+	// Note: This test cannot be parallel, as it inspects the size of the shared
+	// map of connectors in the driver. There is no guarantee how many connectors
+	// will be open when the test is running, if there are also other tests running
+	// in parallel.
+
+	db, _, teardown := setupTestDBConnection(t)
+	defer teardown()
+
+	ctx := context.Background()
+	conn, err := db.Conn(ctx)
+	if err != nil {
+		t.Fatalf("failed to get a connection: %v", err)
+	}
+	_ = conn.Close()
+	connectors := db.Driver().(*Driver).connectors
+	if g, w := len(connectors), 1; g != w {
+		t.Fatal("underlying connector has not been created")
+	}
+	var connector *connector
+	for _, v := range connectors {
+		connector = v
+	}
+	if connector.closed {
+		t.Fatal("connector is closed")
+	}
+
+	if err := db.Close(); err != nil {
+		t.Fatalf("failed to close connector: %v", err)
+	}
+	_, err = db.Conn(ctx)
+	if err == nil {
+		t.Fatal("missing error for getting a connection from a closed connector")
+	}
+	if g, w := err.Error(), "sql: database is closed"; g != w {
+		t.Fatalf("error mismatch for getting a connection from a closed connector\n Got: %v\nWant: %v", g, w)
+	}
+	// Verify that the underlying connector also has been closed.
+	if g, w := len(connectors), 0; g != w {
+		t.Fatal("underlying connector has not been closed")
+	}
+	if !connector.closed {
+		t.Fatal("connector is not closed")
+	}
 }
 
 func numeric(v string) big.Rat {
diff --git a/examples/ddl-batches/main.go b/examples/ddl-batches/main.go
index e32fa5ae..f2d1ce3e 100644
--- a/examples/ddl-batches/main.go
+++ b/examples/ddl-batches/main.go
@@ -29,9 +29,9 @@ import (
 // It is therefore recommended that DDL statements are always executed in batches whenever possible.
 //
 // DDL batches can be executed in two ways using the Spanner go sql driver:
-// 1. By executing the SQL statements `START BATCH DDL` and `RUN BATCH`.
-// 2. By unwrapping the Spanner specific driver interface spannerdriver.Driver and calling the
-//    spannerdriver.Driver#StartBatchDDL and spannerdriver.Driver#RunBatch methods.
+//  1. By executing the SQL statements `START BATCH DDL` and `RUN BATCH`.
+//  2. By unwrapping the Spanner specific driver interface spannerdriver.Driver and calling the
+//     spannerdriver.Driver#StartBatchDDL and spannerdriver.Driver#RunBatch methods.
 //
 // This sample shows how to use both possibilities.
 //
diff --git a/examples/dml-batches/main.go b/examples/dml-batches/main.go
index cf167e67..73a0a41e 100644
--- a/examples/dml-batches/main.go
+++ b/examples/dml-batches/main.go
@@ -31,9 +31,9 @@ var createTableStatement = "CREATE TABLE Singers (SingerId INT64, Name STRING(MA
 // that are needed.
 //
 // DML batches can be executed in two ways using the Spanner go sql driver:
-// 1. By executing the SQL statements `START BATCH DML` and `RUN BATCH`.
-// 2. By unwrapping the Spanner specific driver interface spannerdriver.Driver and calling the
-//    spannerdriver.Driver#StartBatchDML and spannerdriver.Driver#RunBatch methods.
+//  1. By executing the SQL statements `START BATCH DML` and `RUN BATCH`.
+//  2. By unwrapping the Spanner specific driver interface spannerdriver.Driver and calling the
+//     spannerdriver.Driver#StartBatchDML and spannerdriver.Driver#RunBatch methods.
 //
 // This sample shows how to use both possibilities.
 //