diff --git a/lib/Drupal/Core/Database/Driver/pgsql/Connection.php b/lib/Drupal/Core/Database/Driver/pgsql/Connection.php
index 9fc1b66d84..b75c1d6562 100644
--- a/lib/Drupal/Core/Database/Driver/pgsql/Connection.php
+++ b/lib/Drupal/Core/Database/Driver/pgsql/Connection.php
@@ -385,11 +385,11 @@ class Connection extends DatabaseConnection {
    */
   public function getFullQualifiedTableName($table) {
     $options = $this->getConnectionOptions();
-    $prefix = $this->tablePrefix($table);
+    $info = $this->schema()->getPrefixInfo($table);
 
     // The fully qualified table name in PostgreSQL is in the form of
-    // <database>.<schema>.<table>, but the schema is handled inside the prefix.
-    return $options['database'] . '.' . $prefix . $table;
+    // <database>.<schema>.<table>.
+    return $options['database'] . '.' . $info['schema'] . '.' . $info['table'];
   }
 
   /**
diff --git a/lib/Drupal/Core/Database/Driver/pgsql/Schema.php b/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
index 766ebfbf35..ab7afab3d5 100644
--- a/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
+++ b/lib/Drupal/Core/Database/Driver/pgsql/Schema.php
@@ -770,7 +770,7 @@ EOD;
     if (!$this->indexExists($table, $name)) {
       return FALSE;
     }
-    
+
     // Add the schema if not using the default one.
     $index_name = $this->ensureIdentifiersLength($table, $name, 'idx');
     if ($this->defaultSchema != 'public') {
diff --git a/lib/Drupal/Core/Database/Schema.php b/lib/Drupal/Core/Database/Schema.php
index 80a68f6e5a..e336398523 100644
--- a/lib/Drupal/Core/Database/Schema.php
+++ b/lib/Drupal/Core/Database/Schema.php
@@ -67,16 +67,16 @@ abstract class Schema implements PlaceholderInterface {
   /**
    * Get information about the table name and schema from the prefix.
    *
-   * @param
+   * @param string $table
    *   Name of table to look prefix up for. Defaults to 'default' because that's
    *   default key for prefix.
-   * @param $add_prefix
+   * @param bool $add_prefix
    *   Boolean that indicates whether the given table name should be prefixed.
    *
-   * @return
+   * @return array
    *   A keyed array with information about the schema, table name and prefix.
    */
-  protected function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
+  public function getPrefixInfo($table = 'default', $add_prefix = TRUE) {
     $info = [
       'schema' => $this->defaultSchema,
       'prefix' => $this->connection->tablePrefix($table),
diff --git a/modules/migrate/src/Plugin/migrate/id_map/Sql.php b/modules/migrate/src/Plugin/migrate/id_map/Sql.php
index 6bdd51ebf0..77ccbf659e 100644
--- a/modules/migrate/src/Plugin/migrate/id_map/Sql.php
+++ b/modules/migrate/src/Plugin/migrate/id_map/Sql.php
@@ -265,7 +265,23 @@ class Sql extends PluginBase implements MigrateIdMapInterface, ContainerFactoryP
    *   The fully qualified map table name.
    */
   public function getQualifiedMapTableName() {
-    return $this->getDatabase()->getFullQualifiedTableName($this->mapTableName);
+    $qualifiedMapTableName = NULL;
+    $connection = $this->getDatabase();
+
+    switch ($connection->databaseType()) {
+      case 'pgsql':
+        // PostgreSQL doesn't support cross DB merges. So only use schema and
+        // prefixed table name.
+        $info = $connection->schema()->getPrefixInfo($this->mapTableName);
+        $qualifiedMapTableName = $info['schema'] . '.' . $info['table'];
+        break;
+
+      default:
+        $qualifiedMapTableName = $connection->getFullQualifiedTableName($this->mapTableName);
+        break;
+    }
+
+    return $qualifiedMapTableName;
   }
 
   /**