diff -u b/core/modules/pgsql/src/Driver/Database/pgsql/Connection.php b/core/modules/pgsql/src/Driver/Database/pgsql/Connection.php
--- b/core/modules/pgsql/src/Driver/Database/pgsql/Connection.php
+++ b/core/modules/pgsql/src/Driver/Database/pgsql/Connection.php
@@ -314,10 +314,11 @@
    */
   public function getFullQualifiedTableName($table) {
     $options = $this->getConnectionOptions();
+    $schema = $options['schema'] ?? 'public';
 
     // The fully qualified table name in PostgreSQL is in the form of
     // <database>.<schema>.<table>.
-    return $options['database'] . '.' . $options['schema'] . '.' . $this->getPrefix() . $table;
+    return $options['database'] . '.' . $schema . '.' . $this->getPrefix() . $table;;
   }
 
   /**
diff -u b/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php b/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php
--- b/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php
+++ b/core/modules/pgsql/src/Driver/Database/pgsql/Schema.php
@@ -131,16 +131,11 @@
     // Generate a key to reference this table's information on.
     $key = $this->connection->prefixTables('{' . $table . '}');
-    $prefixInfo = $this->getPrefixInfo($table);
-    $prefixed_table = $prefixInfo['table'];
 
     // Take into account that temporary tables are stored in a different schema.
     // \Drupal\Core\Database\Connection::generateTemporaryTableName() sets the
     // 'db_temporary_' prefix to all temporary tables.
-    if (strpos($prefixed_table, 'db_temporary_') === FALSE) {
-      $key = $prefixInfo['schema'] . '.' . $prefixed_table;
+    if (strpos($table, 'db_temporary_') !== FALSE) {
+      $key = $this->getTempNamespaceName() . '.' . $key;
     }
-    else {
-      $key = $this->getTempNamespaceName() . '.' . $prefixed_table;
-    }
 
     if (!isset($this->tableInformation[$key])) {
@@ -175,7 +170,6 @@
         $this->connection->rollbackSavepoint();
         throw $e;
       }
-
       $this->connection->releaseSavepoint();
 
       // If the table information does not yet exist in the PostgreSQL
@@ -223,7 +217,7 @@
    */
   protected function resetTableInformation($table) {
     $prefixInfo = $this->getPrefixInfo($table);
-    $key = $prefixInfo['schema'] . '.' . $prefixInfo['table'];
+    $key = $this->defaultSchema . '.' . $prefixInfo['table'];
     unset($this->tableInformation[$key]);
   }
 
@@ -564,7 +558,7 @@
 
     // Get the schema and tablename for the old table.
     $prefixInfo = $this->getPrefixInfo($table);
-    $schema = $prefixInfo['schema'];
+    $schema = $this->defaultSchema;
     $table_name = $prefixInfo['table'];
     // Index names and constraint names are global in PostgreSQL, so we need to
     // rename them when renaming the table.
@@ -573,7 +567,13 @@
     foreach ($indexes as $index) {
       // Append the schema to the index name.
       $index_short_name = $index->indexname;
-      $index_full_name = $schema . '.' . $index_short_name;
+      if ($schema != 'public') {
+        $index_full_name = $schema . '.' . $index_short_name;
+        $index_full_name = $this->connection->escapeTable($index_full_name);
+      }
+      else {
+        $index_full_name = '"' . $index_short_name . '"';
+      }
 
       // Get the index type by suffix, e.g. idx/key/pkey.
       $index_type = substr($index_short_name, strrpos($index_short_name, '_') + 1);
@@ -593,7 +593,6 @@
         preg_match('/^' . preg_quote($table_name) . '__(.*)__' . preg_quote($index_type) . '/', $index_short_name, $matches);
         $index_name = $matches[1];
       }
-      $index_full_name = $this->connection->escapeTable($index_full_name);
       $this->connection->query('ALTER INDEX ' . $index_full_name . ' RENAME TO ' . $this->ensureIdentifiersLength($new_name, $index_name, $index_type));
     }
 
diff -u b/core/modules/pgsql/tests/src/Kernel/pgsql/NonPublicSchemaTest.php b/core/modules/pgsql/tests/src/Kernel/pgsql/NonPublicSchemaTest.php
--- b/core/modules/pgsql/tests/src/Kernel/pgsql/NonPublicSchemaTest.php
+++ b/core/modules/pgsql/tests/src/Kernel/pgsql/NonPublicSchemaTest.php
@@ -72,9 +72,15 @@
       }
     }
 
+    $this->connection = Database::getConnection('default', 'default');
+    Database::removeConnection('testing_fake');
+
     parent::tearDown();
   }
 
+  /**
+   * Create sample data to test with alternative schema name.
+   */
   protected function createSampleData(): void {
     $this->connection->insert('faking_table')
       ->fields(
@@ -103,11 +109,13 @@
 
   /**
    * @covers \Drupal\Core\Database\Driver\pgsql\Schema::extensionExists
+   * @covers \Drupal\Core\Database\Driver\pgsql\Schema::tableExists
    */
   public function testPgsqlExtensionExists(): void {
+    // Check if PG_trgm extension is present.
+    $this->assertTrue($this->connection->schema()->extensionExists('pg_trgm'));
     // Asserting that the Schema testing_fake exist in the database.
     $this->assertCount(1, \Drupal::database()->query("SELECT * FROM pg_catalog.pg_namespace WHERE nspname = 'testing_fake'")->fetchAll());
-
     $this->assertTrue($this->connection->schema()->tableExists('faking_table'));
 
     // Hardcoded assertion that we created the table in the non-public schema.