diff --git a/lib/Doctrine/ORM/Query/SqlWalker.php b/lib/Doctrine/ORM/Query/SqlWalker.php
index 9c4ac2a88..6fb4df5b1 100644
--- a/lib/Doctrine/ORM/Query/SqlWalker.php
+++ b/lib/Doctrine/ORM/Query/SqlWalker.php
@@ -870,6 +870,19 @@ class SqlWalker implements TreeWalker
      * @return string
      */
     public function walkRangeVariableDeclaration($rangeVariableDeclaration)
+    {
+        return $this->generateRangeVariableDeclarationSQL($rangeVariableDeclaration, false);
+    }
+
+    /**
+     * Generate appropriate SQL for RangeVariableDeclaration AST node
+     *
+     * @param AST\RangeVariableDeclaration $rangeVariableDeclaration
+     * @param bool $buildNestedJoins
+     *
+     * @return string
+     */
+    private function generateRangeVariableDeclarationSQL($rangeVariableDeclaration, $buildNestedJoins)
     {
         $class    = $this->em->getClassMetadata($rangeVariableDeclaration->abstractSchemaName);
         $dqlAlias = $rangeVariableDeclaration->aliasIdentificationVariable;
@@ -885,7 +898,11 @@ class SqlWalker implements TreeWalker
         );
 
         if ($class->isInheritanceTypeJoined()) {
-            $sql .= $this->_generateClassTableInheritanceJoins($class, $dqlAlias);
+            if ($buildNestedJoins) {
+                $sql = '(' . $sql . $this->_generateClassTableInheritanceJoins($class, $dqlAlias) . ')';
+            } else {
+                $sql .= $this->_generateClassTableInheritanceJoins($class, $dqlAlias);
+            }
         }
 
         return $sql;
@@ -1121,16 +1138,17 @@ class SqlWalker implements TreeWalker
             : ' INNER JOIN ';
 
         switch (true) {
-            case ($joinDeclaration instanceof \Doctrine\ORM\Query\AST\RangeVariableDeclaration):
+            case ($joinDeclaration instanceof AST\RangeVariableDeclaration):
                 $class      = $this->em->getClassMetadata($joinDeclaration->abstractSchemaName);
                 $dqlAlias   = $joinDeclaration->aliasIdentificationVariable;
                 $tableAlias = $this->getSQLTableAlias($class->table['name'], $dqlAlias);
                 $condition = '(' . $this->walkConditionalExpression($join->conditionalExpression) . ')';
-                $condExprConjunction = ($class->isInheritanceTypeJoined() && $joinType != AST\Join::JOIN_TYPE_LEFT && $joinType != AST\Join::JOIN_TYPE_LEFTOUTER)
+                $isUnconditionalJoin = empty($conditions);
+                $condExprConjunction = ($class->isInheritanceTypeJoined() && $joinType != AST\Join::JOIN_TYPE_LEFT && $joinType != AST\Join::JOIN_TYPE_LEFTOUTER && $isUnconditionalJoin)
                     ? ' AND '
                     : ' ON ';
 
-                $sql .= $this->walkRangeVariableDeclaration($joinDeclaration);
+                $sql .= $this->generateRangeVariableDeclarationSQL($joinDeclaration, !$isUnconditionalJoin);
 
                 $conditions = array($condition);
 
@@ -1151,7 +1169,7 @@ class SqlWalker implements TreeWalker
                 $sql .= $condExprConjunction . implode(' AND ', $conditions);
                 break;
 
-            case ($joinDeclaration instanceof \Doctrine\ORM\Query\AST\JoinAssociationDeclaration):
+            case ($joinDeclaration instanceof AST\JoinAssociationDeclaration):
                 $sql .= $this->walkJoinAssociationDeclaration($joinDeclaration, $joinType, $join->conditionalExpression);
                 break;
         }
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6464Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6464Test.php
new file mode 100644
index 000000000..adc6f7b16
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH6464Test.php
@@ -0,0 +1,76 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+/**
+ * @group GH-6464
+ */
+class GH6464Test extends OrmFunctionalTestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    protected function setUp()
+    {
+        parent::setUp();
+
+        $this->_schemaTool->createSchema([
+            $this->_em->getClassMetadata(GH6464Post::class),
+            $this->_em->getClassMetadata(GH6464User::class),
+            $this->_em->getClassMetadata(GH6464Author::class),
+        ]);
+    }
+
+    /**
+     * Verifies that SqlWalker generates valid SQL for an INNER JOIN to CTI table
+     *
+     * SqlWalker needs to generate nested INNER JOIN statements, otherwise there would be INNER JOIN
+     * statements without an ON clause, which are valid on e.g. MySQL but rejected by PostgreSQL.
+     */
+    public function testIssue()
+    {
+        $query = $this->_em->createQueryBuilder()
+            ->select('p')
+            ->from(GH6464Post::class, 'p')
+            ->innerJoin(GH6464Author::class, 'a', 'WITH', 'p.authorId = a.id')
+            ->getQuery();
+
+        $this->assertNotRegExp(
+            '/INNER JOIN \w+ \w+ INNER JOIN/',
+            $query->getSQL(),
+            'As of GH-6464, every INNER JOIN should have an ON clause, which is missing here'
+        );
+
+        // Query shouldn't yield a result, yet it shouldn't crash (anymore)
+        $this->assertEquals([], $query->getResult());
+    }
+}
+
+/** @Entity */
+class GH6464Post
+{
+    /** @Id @Column(type="integer") @GeneratedValue */
+    public $id;
+
+    /** @Column(type="integer") */
+    public $authorId;
+}
+
+/**
+ * @Entity
+ * @InheritanceType("JOINED")
+ * @DiscriminatorColumn(name="discr", type="string")
+ * @DiscriminatorMap({"author" = "GH6464Author"})
+ */
+abstract class GH6464User
+{
+    /** @Id @Column(type="integer") @GeneratedValue */
+    public $id;
+}
+
+/** @Entity */
+class GH6464Author extends GH6464User
+{
+}
diff --git a/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php b/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php
index a3a34f822..68fdd3b38 100644
--- a/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php
+++ b/tests/Doctrine/Tests/ORM/Query/SelectSqlGenerationTest.php
@@ -153,12 +153,12 @@ class SelectSqlGenerationTest extends \Doctrine\Tests\OrmTestCase
     {
         $this->assertSqlGeneration(
             'SELECT e FROM Doctrine\Tests\Models\Company\CompanyEmployee e JOIN Doctrine\Tests\Models\Company\CompanyManager m WITH e.id = m.id',
-            'SELECT c0_.id AS id_0, c0_.name AS name_1, c1_.salary AS salary_2, c1_.department AS department_3, c1_.startDate AS startDate_4, c0_.discr AS discr_5 FROM company_employees c1_ INNER JOIN company_persons c0_ ON c1_.id = c0_.id INNER JOIN company_managers c2_ INNER JOIN company_employees c4_ ON c2_.id = c4_.id INNER JOIN company_persons c3_ ON c2_.id = c3_.id AND (c0_.id = c3_.id)'
+            'SELECT c0_.id AS id_0, c0_.name AS name_1, c1_.salary AS salary_2, c1_.department AS department_3, c1_.startDate AS startDate_4, c0_.discr AS discr_5 FROM company_employees c1_ INNER JOIN company_persons c0_ ON c1_.id = c0_.id INNER JOIN (company_managers c2_ INNER JOIN company_employees c4_ ON c2_.id = c4_.id INNER JOIN company_persons c3_ ON c2_.id = c3_.id) ON (c0_.id = c3_.id)'
         );
 
         $this->assertSqlGeneration(
             'SELECT e FROM Doctrine\Tests\Models\Company\CompanyEmployee e LEFT JOIN Doctrine\Tests\Models\Company\CompanyManager m WITH e.id = m.id',
-            'SELECT c0_.id AS id_0, c0_.name AS name_1, c1_.salary AS salary_2, c1_.department AS department_3, c1_.startDate AS startDate_4, c0_.discr AS discr_5 FROM company_employees c1_ INNER JOIN company_persons c0_ ON c1_.id = c0_.id LEFT JOIN company_managers c2_ INNER JOIN company_employees c4_ ON c2_.id = c4_.id INNER JOIN company_persons c3_ ON c2_.id = c3_.id ON (c0_.id = c3_.id)'
+            'SELECT c0_.id AS id_0, c0_.name AS name_1, c1_.salary AS salary_2, c1_.department AS department_3, c1_.startDate AS startDate_4, c0_.discr AS discr_5 FROM company_employees c1_ INNER JOIN company_persons c0_ ON c1_.id = c0_.id LEFT JOIN (company_managers c2_ INNER JOIN company_employees c4_ ON c2_.id = c4_.id INNER JOIN company_persons c3_ ON c2_.id = c3_.id) ON (c0_.id = c3_.id)'
         );
     }
 
@@ -2165,7 +2165,7 @@ class SelectSqlGenerationTest extends \Doctrine\Tests\OrmTestCase
         // the where clause when not joining onto that table
         $this->assertSqlGeneration(
             'SELECT c FROM Doctrine\Tests\Models\Company\CompanyContract c LEFT JOIN Doctrine\Tests\Models\Company\CompanyEmployee e WITH e.id = c.salesPerson WHERE c.completed = true',
-            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6 FROM company_contracts c0_ LEFT JOIN company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id ON (c2_.id = c0_.salesPerson_id) WHERE (c0_.completed = 1) AND c0_.discr IN ('fix', 'flexible', 'flexultra')"
+            "SELECT c0_.id AS id_0, c0_.completed AS completed_1, c0_.fixPrice AS fixPrice_2, c0_.hoursWorked AS hoursWorked_3, c0_.pricePerHour AS pricePerHour_4, c0_.maxPrice AS maxPrice_5, c0_.discr AS discr_6 FROM company_contracts c0_ LEFT JOIN (company_employees c1_ INNER JOIN company_persons c2_ ON c1_.id = c2_.id) ON (c2_.id = c0_.salesPerson_id) WHERE (c0_.completed = 1) AND c0_.discr IN ('fix', 'flexible', 'flexultra')"
         );
     }