diff --git a/lib/Doctrine/ORM/Query/Parser.php b/lib/Doctrine/ORM/Query/Parser.php
index 48b13df64a..d52f3ce1b2 100644
--- a/lib/Doctrine/ORM/Query/Parser.php
+++ b/lib/Doctrine/ORM/Query/Parser.php
@@ -2924,6 +2924,10 @@ public function StringPrimary()
             case Lexer::T_COALESCE:
             case Lexer::T_NULLIF:
                 return $this->CaseExpression();
+            default:
+                if ($this->isAggregateFunction($lookaheadType)) {
+                    return $this->AggregateExpression();
+                }
         }
 
         $this->syntaxError(
diff --git a/tests/Doctrine/Tests/ORM/Functional/Ticket/GH7286Test.php b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH7286Test.php
new file mode 100644
index 0000000000..75e626f336
--- /dev/null
+++ b/tests/Doctrine/Tests/ORM/Functional/Ticket/GH7286Test.php
@@ -0,0 +1,140 @@
+<?php
+
+namespace Doctrine\Tests\ORM\Functional\Ticket;
+
+use Doctrine\ORM\Query\AST\Functions\FunctionNode;
+use Doctrine\ORM\Query\AST\Node;
+use Doctrine\ORM\Query\Lexer;
+use Doctrine\ORM\Query\Parser;
+use Doctrine\ORM\Query\SqlWalker;
+use Doctrine\Tests\OrmFunctionalTestCase;
+
+final class GH7286Test extends OrmFunctionalTestCase
+{
+    /**
+     * {@inheritDoc}
+     */
+    protected function setUp() : void
+    {
+        parent::setUp();
+
+        $this->setUpEntitySchema(
+            [
+                GH7286Entity::class,
+            ]
+        );
+
+        $this->_em->persist(new GH7286Entity('foo', 1));
+        $this->_em->persist(new GH7286Entity('foo', 2));
+        $this->_em->persist(new GH7286Entity('bar', 3));
+        $this->_em->persist(new GH7286Entity(null, 4));
+        $this->_em->flush();
+        $this->_em->clear();
+    }
+
+    public function testAggregateExpressionInFunction() : void
+    {
+        $query = $this->_em->createQuery(
+            'SELECT CONCAT(e.type, MIN(e.version)) pair'
+            . ' FROM ' . GH7286Entity::class . ' e'
+            . ' WHERE e.type IS NOT NULL'
+            . ' GROUP BY e.type'
+            . ' ORDER BY e.type'
+        );
+
+        self::assertSame(
+            [
+                ['pair' => 'bar3'],
+                ['pair' => 'foo1'],
+            ],
+            $query->getArrayResult()
+        );
+    }
+
+    /**
+     * @group DDC-1091
+     */
+    public function testAggregateFunctionInCustomFunction() : void
+    {
+        $this->_em->getConfiguration()->addCustomStringFunction('CC', GH7286CustomConcat::class);
+
+        $entityA = new GH7286Entity('foo', 1);
+        $this->_em->persist($entityA);
+        $this->_em->flush();
+        $this->_em->clear();
+
+        $query = $this->_em->createQuery(
+            'SELECT CC(e.type, MIN(e.version)) pair'
+            . ' FROM ' . GH7286Entity::class . ' e'
+            . ' WHERE e.type IS NOT NULL AND e.type != :type'
+            . ' GROUP BY e.type'
+        );
+        $query->setParameter('type', 'bar');
+
+        self::assertSame(
+            ['pair' => 'foo1'],
+            $query->getSingleResult()
+        );
+    }
+}
+
+/**
+ * @Entity
+ */
+class GH7286Entity
+{
+    /**
+     * @Id
+     * @Column(type="integer")
+     * @GeneratedValue
+     * @var int
+     */
+    public $id;
+
+    /**
+     * @Column(nullable=true)
+     * @var string|null
+     */
+    public $type;
+
+    /**
+     * @Column(type="integer")
+     * @var int
+     */
+    public $version;
+
+    public function __construct(?string $type, int $version)
+    {
+        $this->type    = $type;
+        $this->version = $version;
+    }
+}
+
+class GH7286CustomConcat extends FunctionNode
+{
+    /** @var Node */
+    private $first;
+
+    /** @var Node */
+    private $second;
+
+    public function parse(Parser $parser) : void
+    {
+        $parser->match(Lexer::T_IDENTIFIER);
+        $parser->match(Lexer::T_OPEN_PARENTHESIS);
+
+        $this->first = $parser->StringPrimary();
+        $parser->match(Lexer::T_COMMA);
+        $this->second = $parser->StringPrimary();
+
+        $parser->match(Lexer::T_CLOSE_PARENTHESIS);
+    }
+
+    public function getSql(SqlWalker $walker) : string
+    {
+        return $walker->getConnection()->getDatabasePlatform()->getConcatExpression(
+            $this->first->dispatch($walker),
+            $this->second->dispatch($walker)
+        );
+    }
+}
diff --git a/tests/Doctrine/Tests/ORM/Query/LanguageRecognitionTest.php b/tests/Doctrine/Tests/ORM/Query/LanguageRecognitionTest.php
index 064c0a799c..fe3b298cbf 100644
--- a/tests/Doctrine/Tests/ORM/Query/LanguageRecognitionTest.php
+++ b/tests/Doctrine/Tests/ORM/Query/LanguageRecognitionTest.php
@@ -708,6 +708,13 @@ public function testNewLiteralWithSubselectExpression()
     {
         $this->assertValidDQL("SELECT new " . __NAMESPACE__ . "\\DummyStruct(u.id, 'foo', (SELECT 1 FROM Doctrine\Tests\Models\CMS\CmsUser su), true) FROM Doctrine\Tests\Models\CMS\CmsUser u");
     }
+
+    public function testStringPrimaryAcceptsAggregateExpression() : void
+    {
+        $this->assertValidDQL(
+            'SELECT CONCAT(a.topic, MAX(a.version)) last FROM Doctrine\Tests\Models\CMS\CmsArticle a GROUP BY a'
+        );
+    }
 }
 
 /** @Entity */