diff --git a/stdlib/sql.go b/stdlib/sql.go
index 71380e98..a0bc6182 100644
--- a/stdlib/sql.go
+++ b/stdlib/sql.go
@@ -169,6 +169,7 @@ func GetDefaultDriver() driver.Driver {
 type Driver struct {
 	configMutex sync.Mutex
 	configs     map[string]*pgx.ConnConfig
+	sequence    int
 }
 
 func (d *Driver) Open(name string) (driver.Conn, error) {
@@ -188,7 +189,8 @@ func (d *Driver) OpenConnector(name string) (driver.Connector, error) {
 
 func (d *Driver) registerConnConfig(c *pgx.ConnConfig) string {
 	d.configMutex.Lock()
-	connStr := fmt.Sprintf("registeredConnConfig%d", len(d.configs))
+	connStr := fmt.Sprintf("registeredConnConfig%d", d.sequence)
+	d.sequence++
 	d.configs[connStr] = c
 	d.configMutex.Unlock()
 	return connStr
diff --git a/stdlib/sql_test.go b/stdlib/sql_test.go
index 1365f230..5131194c 100644
--- a/stdlib/sql_test.go
+++ b/stdlib/sql_test.go
@@ -1067,8 +1067,15 @@ func TestRegisterConnConfig(t *testing.T) {
 	logger := &testLogger{}
 	connConfig.Logger = logger
 
+	// Issue 947: Register and unregister a ConnConfig and ensure that the
+	// returned connection string is not reused.
 	connStr := stdlib.RegisterConnConfig(connConfig)
+	require.Equal(t, "registeredConnConfig0", connStr)
+	stdlib.UnregisterConnConfig(connStr)
+
+	connStr = stdlib.RegisterConnConfig(connConfig)
 	defer stdlib.UnregisterConnConfig(connStr)
+	require.Equal(t, "registeredConnConfig1", connStr)
 
 	db, err := sql.Open("pgx", connStr)
 	require.NoError(t, err)